diff --git a/packages/data-models/flowTypes.ts b/packages/data-models/flowTypes.ts
index 215cf2906e..9b568bfe78 100644
--- a/packages/data-models/flowTypes.ts
+++ b/packages/data-models/flowTypes.ts
@@ -340,17 +340,24 @@ export namespace FlowTypes {
     _evalContext?: { itemContext: TemplateRowItemEvalContext }; // force specific context variables when calculating eval statements (such as loop items)
     __EMPTY?: any; // empty cells (can be removed after pr 679 merged)
   }
+
   export type IDynamicField = { [key: string]: IDynamicField | TemplateRowDynamicEvaluator[] };
 
-  export interface TemplateRowItemEvalContext {
+  export interface TemplateRowItemEvalContextMetadata {
     // item metadata
     _id: string;
     _index: number;
     _first: boolean;
     _last: boolean;
-    // item data
-    [key: string]: any;
   }
+  // Enumerable list of metadata columns for use by processing functions
+  export const TEMPLATE_ROW_ITEM_METADATA_FIELDS: Array<keyof TemplateRowItemEvalContextMetadata> =
+    ["_id", "_index", "_first", "_last"];
+
+  // General interface for row items which can contain any key-value pairs with metadata
+  export type TemplateRowItemEvalContext = TemplateRowItemEvalContextMetadata & {
+    [key: string]: any;
+  };
 
   type IDynamicPrefix = IAppConfig["DYNAMIC_PREFIXES"][number];
 
diff --git a/src/app/shared/components/template/components/data-items/data-items.component.ts b/src/app/shared/components/template/components/data-items/data-items.component.ts
index 7f94e2756f..b32c9275ee 100644
--- a/src/app/shared/components/template/components/data-items/data-items.component.ts
+++ b/src/app/shared/components/template/components/data-items/data-items.component.ts
@@ -7,7 +7,10 @@ import {
   OnDestroy,
 } from "@angular/core";
 import { debounceTime, Subscription } from "rxjs";
-import { DynamicDataService } from "src/app/shared/services/dynamic-data/dynamic-data.service";
+import {
+  DynamicDataService,
+  ISetItemContext,
+} from "src/app/shared/services/dynamic-data/dynamic-data.service";
 import { FlowTypes } from "../../models";
 import { ItemProcessor } from "../../processors/item";
 import { TemplateRowService } from "../../services/instance/template-row.service";
@@ -96,8 +99,9 @@ export class TmplDataItemsComponent extends TemplateBaseComponent implements OnD
     const itemDataIDs = itemData.map((item) => item.id);
     // Reassign metadata fields previously assigned by item as rendered row count may have changed
     return templateRows.map((r) => {
+      const itemId = r._evalContext.itemContext._id;
       // Map the row item context to the original list of items rendered to know position in item list.
-      const itemIndex = itemDataIDs.indexOf(r._evalContext.itemContext._id);
+      const itemIndex = itemDataIDs.indexOf(itemId);
       // Update metadata fields as _first, _last and index may have changed based on dynamic updates
       r._evalContext.itemContext = {
         ...r._evalContext.itemContext,
@@ -108,14 +112,19 @@ export class TmplDataItemsComponent extends TemplateBaseComponent implements OnD
       // Update any action list set_item args to contain name of current data list and item id
       // and set_items action to include all currently displayed rows
       if (r.action_list) {
+        const setItemContext: ISetItemContext = {
+          flow_name: this.dataListName,
+          itemDataIDs,
+          currentItemId: itemId,
+        };
         r.action_list = r.action_list.map((a) => {
           if (a.action_id === "set_item") {
-            a.args = [this.dataListName, r._evalContext.itemContext._id];
+            a.args = [setItemContext];
           }
           if (a.action_id === "set_items") {
             // TODO - add a check for @item refs and replace parameter list with correct values
             // for each individual item (default will be just to pick the first)
-            a.args = [this.dataListName, itemDataIDs];
+            a.args = [setItemContext];
           }
           return a;
         });
diff --git a/src/app/shared/components/template/services/template-calc.spec.ts b/src/app/shared/components/template/services/template-calc.service.spec.ts
similarity index 88%
rename from src/app/shared/components/template/services/template-calc.spec.ts
rename to src/app/shared/components/template/services/template-calc.service.spec.ts
index 344a5affad..2752062482 100644
--- a/src/app/shared/components/template/services/template-calc.spec.ts
+++ b/src/app/shared/components/template/services/template-calc.service.spec.ts
@@ -1,3 +1,19 @@
+import { ICalcContext, TemplateCalcService } from "./template-calc.service";
+
+export class MockTemplateCalcService implements Partial<TemplateCalcService> {
+  public async ready(): Promise<boolean> {
+    return true;
+  }
+
+  public getCalcContext(): ICalcContext {
+    return {
+      thisCtxt: {},
+      globalConstants: {},
+      globalFunctions: {},
+    };
+  }
+}
+
 /**
  * TODO - Add testing data and methods
  * 
diff --git a/src/app/shared/components/template/services/template-field.service.spec.ts b/src/app/shared/components/template/services/template-field.service.spec.ts
index f2ae3e1291..dcfd73f763 100644
--- a/src/app/shared/components/template/services/template-field.service.spec.ts
+++ b/src/app/shared/components/template/services/template-field.service.spec.ts
@@ -3,6 +3,8 @@ import { TestBed } from "@angular/core/testing";
 import { TemplateFieldService } from "./template-field.service";
 import type { PromiseExtended } from "dexie";
 import { booleanStringToBoolean } from "src/app/shared/utils";
+import { ErrorHandlerService } from "src/app/shared/services/error-handler/error-handler.service";
+import { MockErrorHandlerService } from "src/app/shared/services/error-handler/error-handler.service.spec";
 
 /** Mock calls for field values from the template field service to return test data */
 export class MockTemplateFieldService implements Partial<TemplateFieldService> {
@@ -27,11 +29,13 @@ export class MockTemplateFieldService implements Partial<TemplateFieldService> {
 describe("TemplateFieldService", () => {
   let service: TemplateFieldService;
 
-  beforeEach(() => {
+  beforeEach(async () => {
     TestBed.configureTestingModule({
       imports: [HttpClientTestingModule],
+      providers: [{ provide: ErrorHandlerService, useValue: new MockErrorHandlerService() }],
     });
     service = TestBed.inject(TemplateFieldService);
+    await service.ready();
   });
 
   it("should be created", () => {
diff --git a/src/app/shared/components/template/services/template-translate.service.spec.ts b/src/app/shared/components/template/services/template-translate.service.spec.ts
index e293081bfa..249e87c97f 100644
--- a/src/app/shared/components/template/services/template-translate.service.spec.ts
+++ b/src/app/shared/components/template/services/template-translate.service.spec.ts
@@ -12,7 +12,7 @@ export class MockTemplateTranslateService implements Partial<TemplateTranslateSe
   }
 }
 
-describe("TaskService", () => {
+describe("TemplateTranslateService", () => {
   let service: TemplateTranslateService;
 
   beforeEach(() => {
diff --git a/src/app/shared/components/template/services/template-variables.service.spec.ts b/src/app/shared/components/template/services/template-variables.service.spec.ts
new file mode 100644
index 0000000000..259296d750
--- /dev/null
+++ b/src/app/shared/components/template/services/template-variables.service.spec.ts
@@ -0,0 +1,181 @@
+import { TestBed } from "@angular/core/testing";
+import { IVariableContext, TemplateVariablesService } from "./template-variables.service";
+import { HttpClientTestingModule } from "@angular/common/http/testing";
+import { TemplateFieldService } from "./template-field.service";
+import { MockTemplateFieldService } from "./template-field.service.spec";
+import { AppDataService } from "src/app/shared/services/data/app-data.service";
+import { CampaignService } from "src/app/feature/campaign/campaign.service";
+import { MockAppDataService } from "src/app/shared/services/data/app-data.service.spec";
+import { TemplateCalcService } from "./template-calc.service";
+import { MockTemplateCalcService } from "./template-calc.service.spec";
+
+const MOCK_APP_DATA = {};
+
+// Fields populated to mock field service
+const MOCK_FIELDS = {
+  _app_language: "gb_en",
+  _app_skin: "default",
+  string_field: "test_string_value",
+  number_field: 2,
+};
+
+const MOCK_CONTEXT_BASE: IVariableContext = {
+  // Assume the row will have a dynamic 'field' entry
+  field: "value",
+  row: {
+    type: "text",
+    value: "",
+    name: "test_row",
+    _nested_name: "test_row",
+  },
+  templateRowMap: {},
+  calcContext: {
+    globalConstants: {},
+    globalFunctions: {},
+    thisCtxt: {
+      fields: MOCK_FIELDS,
+      local: {},
+    },
+  },
+};
+
+const TEST_FIELD_CONTEXT: IVariableContext = {
+  ...MOCK_CONTEXT_BASE,
+  row: {
+    ...MOCK_CONTEXT_BASE.row,
+    value: "Hello @fields.string_field",
+    _dynamicFields: {
+      value: [
+        {
+          fullExpression: "Hello @fields.string_field",
+          matchedExpression: "@fields.string_field",
+          type: "fields",
+          fieldName: "string_field",
+        },
+      ],
+    },
+  },
+};
+
+// Context adapted from this debug template:
+// https://docs.google.com/spreadsheets/d/1tL6CPHEIW-GPMYjdhVKQToy_hZ1H5qNIBkkh9XnA5QM/edit#gid=114708400
+const TEST_ITEM_CONTEXT: IVariableContext = {
+  ...MOCK_CONTEXT_BASE,
+  row: {
+    ...MOCK_CONTEXT_BASE.row,
+    value: "@item._index + 1",
+    // NOTE - any evaluated fields should appea
+    _dynamicFields: {
+      value: [
+        {
+          fullExpression: "@item._index + 1",
+          matchedExpression: "@item._index",
+          type: "item",
+          fieldName: "_index",
+        },
+      ],
+    },
+  },
+  itemContext: {
+    id: "id1",
+    number: 1,
+    string: "hello",
+    boolean: true,
+    _index: 0,
+    _id: "id1",
+    _first: true,
+    _last: false,
+  },
+};
+
+/**
+ * Call standalone tests via:
+ * yarn ng test --include src/app/shared/components/template/services/template-variables.service.spec.ts
+ */
+describe("TemplateVariablesService", () => {
+  let service: TemplateVariablesService;
+  let getNextCampaignRowsSpy: jasmine.Spy<jasmine.Func>;
+
+  beforeEach(async () => {
+    getNextCampaignRowsSpy = jasmine.createSpy();
+    TestBed.configureTestingModule({
+      imports: [HttpClientTestingModule],
+      providers: [
+        {
+          provide: TemplateFieldService,
+          useValue: new MockTemplateFieldService(MOCK_FIELDS),
+        },
+        {
+          provide: AppDataService,
+          useValue: new MockAppDataService(MOCK_APP_DATA),
+        },
+        {
+          provide: TemplateCalcService,
+          useValue: new MockTemplateCalcService(),
+        },
+        // Mock single method from campaign service called
+        {
+          provide: CampaignService,
+          useValue: {
+            ready: async () => {
+              return true;
+            },
+            getNextCampaignRows: getNextCampaignRowsSpy,
+          },
+        },
+      ],
+    });
+    service = TestBed.inject(TemplateVariablesService);
+    await service.ready();
+  });
+
+  it("should be created", () => {
+    expect(service).toBeTruthy();
+  });
+
+  it("Evaluates PLH Data String", async () => {
+    console.log({ TEST_FIELD_CONTEXT });
+    const res = await service.evaluatePLHData("Hello @fields.string_field", TEST_FIELD_CONTEXT);
+    expect(res).toEqual("Hello test_string_value");
+    // Data will only be evaluated if it has been pre-parsed, extracting dynamic references
+    // If not returns raw value
+    delete TEST_FIELD_CONTEXT.row._dynamicFields;
+    const resWithoutDynamicContext = await service.evaluatePLHData(
+      "@fields.string_field",
+      TEST_FIELD_CONTEXT
+    );
+    expect(resWithoutDynamicContext).toEqual("@fields.string_field");
+    /** 
+     * TODO - include all edge cases, e.g. raw, item, calc, deep-nested, object, array etc.
+    const res = await service.evaluatePLHData(["@fields.string_field"], MOCK_CONTEXT);
+    expect(res).toEqual({ 1: "test_string_value" });
+    const res = await service.evaluatePLHData(
+      {
+        nested: "@fields.string_field",
+      },
+      MOCK_CONTEXT
+    );
+    expect(res).toEqual({ nested: "test_string_value" });
+     */
+  });
+  it("Evaluates condition strings", async () => {
+    // Condition strings are evaluated without any previous pre-parsed dynamic fields
+    const res = await service.evaluateConditionString("@fields.number_field > 3");
+    expect(res).toEqual(false);
+  });
+
+  it("evaluates string containing item variable", async () => {
+    const MOCK_ITEM_STRING = "@item._index + 1";
+    // Parse expression when item context included
+    const resWithItemContext = await service.evaluatePLHData(MOCK_ITEM_STRING, TEST_ITEM_CONTEXT);
+    expect(resWithItemContext).toEqual(1);
+    // Retain raw expression if evaluating outside of item context
+    // https://github.com/IDEMSInternational/parenting-app-ui/pull/2215#discussion_r1514757364
+    delete TEST_ITEM_CONTEXT.itemContext;
+    const resWithoutItemContext = await service.evaluatePLHData(
+      MOCK_ITEM_STRING,
+      TEST_ITEM_CONTEXT
+    );
+    expect(resWithoutItemContext).toEqual(MOCK_ITEM_STRING);
+  });
+});
diff --git a/src/app/shared/components/template/services/template-variables.service.ts b/src/app/shared/components/template/services/template-variables.service.ts
index 75984760e8..cfd818a7ec 100644
--- a/src/app/shared/components/template/services/template-variables.service.ts
+++ b/src/app/shared/components/template/services/template-variables.service.ts
@@ -16,6 +16,8 @@ const log = SHOW_DEBUG_LOGS ? console.log : () => null;
 const log_group = SHOW_DEBUG_LOGS ? console.group : () => null;
 const log_groupEnd = SHOW_DEBUG_LOGS ? console.groupEnd : () => null;
 
+const { TEMPLATE_ROW_ITEM_METADATA_FIELDS } = FlowTypes;
+
 /**
  * Most methods in this class depend on factors relating to the execution context
  * (e.g.row, variables etc.). Store as a single object to make it easier to pass between methods
@@ -120,12 +122,19 @@ export class TemplateVariablesService extends AsyncServiceBase {
   }
 
   /**
-   * Inore evaluation of meta, comment, and specifiedfields.
+   * Ignore evaluation of meta, comment, and specifiedfields.
    * Could provide single list of approved fields, but as dynamic fields also can be found in parameter lists
    * would likely prove too restrictive
    **/
-  private shouldEvaluateField(fieldName: keyof FlowTypes.TemplateRow, omitFields: string[] = []) {
+  private shouldEvaluateField(
+    fieldName: keyof FlowTypes.TemplateRow | keyof FlowTypes.TemplateRowItemEvalContextMetadata,
+    omitFields: string[] = []
+  ) {
     if (omitFields.includes(fieldName)) return false;
+
+    // Evaluate fields that are names of item metadata fields, e.g. "_index", "_id",
+    // E.g. for use in actions such as `click | set_item | _index: @item._index + 1, completed:false`
+    if (TEMPLATE_ROW_ITEM_METADATA_FIELDS.includes(fieldName as any)) return true;
     if (fieldName.startsWith("_")) return false;
     return true;
   }
@@ -183,6 +192,11 @@ export class TemplateVariablesService extends AsyncServiceBase {
         return evaluator.fullExpression.replace(/`/gi, "");
       }
 
+      // Do not evaluate if the appropriate context is not available
+      if (type === "item" && !context.itemContext) {
+        return evaluator.fullExpression;
+      }
+
       // process the main lookup, e.g. @local.some_val, @campaign.some_val
       // NOTE - if parse fail an empty string will be returned
       let { parsedValue, parseSuccess } = await this.processDynamicEvaluator(evaluator, context);
diff --git a/src/app/shared/services/dynamic-data/dynamic-data.service.spec.ts b/src/app/shared/services/dynamic-data/dynamic-data.service.spec.ts
index b9e66c86b0..50ec015cc2 100644
--- a/src/app/shared/services/dynamic-data/dynamic-data.service.spec.ts
+++ b/src/app/shared/services/dynamic-data/dynamic-data.service.spec.ts
@@ -2,7 +2,7 @@ import { TestBed } from "@angular/core/testing";
 import { HttpClientTestingModule } from "@angular/common/http/testing";
 import { firstValueFrom } from "rxjs";
 
-import { DynamicDataService } from "./dynamic-data.service";
+import { DynamicDataService, ISetItemContext } from "./dynamic-data.service";
 import { AppDataService } from "../data/app-data.service";
 import { MockAppDataService } from "../data/app-data.service.spec";
 
@@ -12,6 +12,12 @@ const TEST_DATA_ROWS = [
 ];
 type ITestRow = (typeof TEST_DATA_ROWS)[number];
 
+const SET_ITEM_CONTEXT: ISetItemContext = {
+  flow_name: "test_flow",
+  itemDataIDs: ["id1", "id2"],
+  currentItemId: "id1",
+};
+
 /**
  * Call standalone tests via:
  * yarn ng test --include src/app/shared/services/dynamic-data/dynamic-data.service.spec.ts
@@ -102,6 +108,41 @@ describe("DynamicDataService", () => {
     expect(res.length).toEqual(20);
   });
 
+  it("sets an item correctly for current item", async () => {
+    await service.setItem({
+      context: SET_ITEM_CONTEXT,
+      writeableProps: { string: "sets an item correctly for current item" },
+    });
+    const obs = await service.query$<any>("data_list", "test_flow");
+    const data = await firstValueFrom(obs);
+    expect(data[0].string).toEqual("sets an item correctly for current item");
+    expect(data[1].string).toEqual("goodbye");
+  });
+
+  it("sets an item correctly for a given _id", async () => {
+    await service.setItem({
+      context: SET_ITEM_CONTEXT,
+      _id: "id2",
+      writeableProps: { string: "sets an item correctly for a given _id" },
+    });
+    const obs = await service.query$<any>("data_list", "test_flow");
+    const data = await firstValueFrom(obs);
+    expect(data[0].string).toEqual("hello");
+    expect(data[1].string).toEqual("sets an item correctly for a given _id");
+  });
+
+  it("sets an item correctly for a given _index", async () => {
+    await service.setItem({
+      context: SET_ITEM_CONTEXT,
+      _index: 1,
+      writeableProps: { string: "sets an item correctly for a given _index" },
+    });
+    const obs = await service.query$<any>("data_list", "test_flow");
+    const data = await firstValueFrom(obs);
+    expect(data[0].string).toEqual("hello");
+    expect(data[1].string).toEqual("sets an item correctly for a given _index");
+  });
+
   // QA
   it("prevents query of non-existent data lists", async () => {
     let errMsg: string;
diff --git a/src/app/shared/services/dynamic-data/dynamic-data.service.ts b/src/app/shared/services/dynamic-data/dynamic-data.service.ts
index 1f47c86473..d54b2b5c48 100644
--- a/src/app/shared/services/dynamic-data/dynamic-data.service.ts
+++ b/src/app/shared/services/dynamic-data/dynamic-data.service.ts
@@ -66,14 +66,24 @@ export class DynamicDataService extends AsyncServiceBase {
   }
   private registerTemplateActionHandlers() {
     this.templateActionRegistry.register({
+      /**
+       * Write properties on the current item (default), or on an explicitly targeted item,
+       * e.g.
+       * click | set_item | completed:true;
+       * click | set_item | _id: @item.id, completed:true;
+       * click | set_item | _index: @item._index + 1, completed:true;
+       */
       set_item: async ({ args, params }) => {
-        const [flow_name, row_id] = args;
-        await this.update("data_list", flow_name, row_id, params);
+        // The data-items component populates the context for evaluating the target item to be updated
+        const context = args[0] as ISetItemContext;
+        // The params come directly from the authored action
+        const { _index, _id, ...writeableProps } = params;
+        await this.setItem({ context, _index, _id, writeableProps });
       },
       set_items: async ({ args, params }) => {
-        const [flow_name, row_ids] = args;
+        const { flow_name, itemDataIDs } = args[0] as ISetItemContext;
         // Hack, no current method for bulk update so make successive (changes debounced in component)
-        for (const row_id of row_ids) {
+        for (const row_id of itemDataIDs) {
           await this.update("data_list", flow_name, row_id, params);
         }
       },
@@ -223,4 +233,47 @@ export class DynamicDataService extends AsyncServiceBase {
     }
     return schema;
   }
+
+  /**
+   * Update an "item", a row within a data-items loop, e.g. as triggered by the set_item action.
+   * If an _id is specified, the row with that ID is updated,
+   * else if an _index is specified, the row with corresponding to the item at that index is updated,
+   * if neither is specified, then the current item (as defined in context) is updated
+   */
+  public async setItem(params: {
+    context: ISetItemContext;
+    /** the index of a specific item to update */
+    _index?: number;
+    /** the id of a specific item to update */
+    _id?: string;
+    /** the property key/values to update on the targeted item */
+    writeableProps: any;
+  }) {
+    const { flow_name, itemDataIDs, currentItemId } = params.context;
+    const { _index, _id, writeableProps } = params;
+
+    let targetRowId = currentItemId;
+    if (_id) {
+      targetRowId = _id;
+    }
+    if (_index !== undefined) {
+      targetRowId = itemDataIDs[_index];
+    }
+
+    if (itemDataIDs.includes(targetRowId)) {
+      await this.update("data_list", flow_name, targetRowId, writeableProps);
+    } else {
+      console.warn(`[SET ITEM] - No item ${_id ? "with ID " + _id : "at index " + _index}`);
+    }
+  }
+}
+
+/** the context for evaluating the target item to be updated, provided by the data-items component */
+export interface ISetItemContext {
+  /** the name of the data_list containing the item to update */
+  flow_name: string;
+  /** an array of the IDs of all the item rows in the loop */
+  itemDataIDs: string[];
+  /** the ID of the current item */
+  currentItemId: string;
 }
diff --git a/src/app/shared/services/error-handler/error-handler.service.spec.ts b/src/app/shared/services/error-handler/error-handler.service.spec.ts
index 943381c9f6..96afdbf7f1 100644
--- a/src/app/shared/services/error-handler/error-handler.service.spec.ts
+++ b/src/app/shared/services/error-handler/error-handler.service.spec.ts
@@ -1,6 +1,7 @@
 import { TestBed } from "@angular/core/testing";
 
 import { ErrorHandlerService } from "./error-handler.service";
+import { FirebaseService } from "../firebase/firebase.service";
 
 /** Mock calls for sheets from the appData service to return test data */
 export class MockErrorHandlerService implements Partial<ErrorHandlerService> {
@@ -16,7 +17,14 @@ describe("ErrorHandlerService", () => {
   let service: ErrorHandlerService;
 
   beforeEach(() => {
-    TestBed.configureTestingModule({});
+    TestBed.configureTestingModule({
+      providers: [
+        {
+          provide: FirebaseService,
+          useValue: {},
+        },
+      ],
+    });
     service = TestBed.inject(ErrorHandlerService);
   });