diff --git a/nextjs-app/__tests__/support/schoolFixtures.ts b/nextjs-app/__tests__/support/schoolFixtures.ts
new file mode 100644
index 0000000..a9a7a31
--- /dev/null
+++ b/nextjs-app/__tests__/support/schoolFixtures.ts
@@ -0,0 +1,332 @@
+/**
+ * Fixtures for the school detail characterization tests.
+ *
+ * Four shapes, each pinning a branch the detail views take:
+ *   primary      — KS2 results, legacy OEIF Ofsted, 3 years of admissions
+ *                  (enough for the year/trend toggle)
+ *   secondary    — KS4 results, Report Card Ofsted, 1 admissions year
+ *                  (no toggle)
+ *   allThrough   — BOTH KS2 and KS4, so the primary content is gated back on
+ *   special      — a special school with an all-zero KS2 row, where the
+ *                  England comparison must be suppressed
+ *
+ * Field names come from lib/types.ts. If TypeScript rejects something here,
+ * the fixture is wrong — never widen the type to accommodate a fixture.
+ */
+
+import type {
+  School, SchoolResult, AbsenceData, OfstedInspection, SchoolCensus,
+  SchoolAdmissions, SchoolDeprivation, SchoolFinance, NationalAverages,
+} from '@/lib/types';
+
+// ---------------------------------------------------------------------------
+// Builders — SchoolResult has 57 required nullable fields, so every fixture
+// starts from an all-null row and overrides only what it is testing.
+// ---------------------------------------------------------------------------
+
+const emptyResult: SchoolResult = {
+  school_id: 1,
+  year: 2024,
+  total_pupils: null, eligible_pupils: null,
+  rwm_expected_pct: null, reading_expected_pct: null, writing_expected_pct: null,
+  maths_expected_pct: null, gps_expected_pct: null, science_expected_pct: null,
+  rwm_high_pct: null, reading_high_pct: null, writing_high_pct: null,
+  maths_high_pct: null, gps_high_pct: null,
+  reading_progress: null, writing_progress: null, maths_progress: null,
+  reading_avg_score: null, maths_avg_score: null, gps_avg_score: null,
+  disadvantaged_pct: null, eal_pct: null, sen_support_pct: null, sen_ehcp_pct: null,
+  stability_pct: null,
+  reading_absence_pct: null, gps_absence_pct: null, maths_absence_pct: null,
+  writing_absence_pct: null, science_absence_pct: null,
+  rwm_expected_boys_pct: null, rwm_expected_girls_pct: null,
+  rwm_high_boys_pct: null, rwm_high_girls_pct: null,
+  rwm_expected_disadvantaged_pct: null, rwm_expected_non_disadvantaged_pct: null,
+  disadvantaged_gap: null,
+  rwm_expected_3yr_pct: null, reading_avg_3yr: null, maths_avg_3yr: null,
+  attainment_8_score: null, progress_8_score: null,
+  progress_8_lower_ci: null, progress_8_upper_ci: null,
+  progress_8_english: null, progress_8_maths: null,
+  progress_8_ebacc: null, progress_8_open: null,
+  english_maths_strong_pass_pct: null, english_maths_standard_pass_pct: null,
+  ebacc_entry_pct: null, ebacc_strong_pass_pct: null, ebacc_standard_pass_pct: null,
+  ebacc_avg_score: null, gcse_grade_91_pct: null, prior_attainment_avg: null,
+};
+
+export function makeResult(overrides: Partial<SchoolResult> = {}): SchoolResult {
+  return { ...emptyResult, ...overrides };
+}
+
+function makeSchool(overrides: Partial<School> = {}): School {
+  return {
+    urn: 123456,
+    school_name: 'Test Primary School',
+    local_authority: 'Westshire',
+    local_authority_code: 900,
+    school_type: 'Community school',
+    school_type_code: 'CY',
+    religious_denomination: 'None',
+    age_range: '4-11',
+    address1: '1 Test Lane',
+    address2: null,
+    town: 'Testville',
+    postcode: 'TE1 1ST',
+    address: '1 Test Lane, Testville, TE1 1ST',
+    latitude: 51.5,
+    longitude: -0.12,
+    phase: 'Primary',
+    gender: 'Mixed',
+    ...overrides,
+  };
+}
+
+const emptyOfsted: OfstedInspection = {
+  framework: null,
+  inspection_date: null,
+  inspection_type: null,
+  overall_effectiveness: null,
+  quality_of_education: null,
+  behaviour_attitudes: null,
+  personal_development: null,
+  leadership_management: null,
+  early_years_provision: null,
+  previous_overall: null,
+  rc_safeguarding_met: null,
+  rc_inclusion: null,
+  rc_curriculum_teaching: null,
+  rc_achievement: null,
+  rc_attendance_behaviour: null,
+  rc_personal_development: null,
+  rc_leadership_governance: null,
+  rc_early_years: null,
+  rc_sixth_form: null,
+  report_url: null,
+};
+
+function makeOfsted(overrides: Partial<OfstedInspection> = {}): OfstedInspection {
+  return { ...emptyOfsted, ...overrides };
+}
+
+function makeAdmissions(overrides: Partial<SchoolAdmissions> = {}): SchoolAdmissions {
+  return {
+    year: 2024,
+    places_offered: 60,
+    total_applications: 210,
+    first_preference_applications: 90,
+    first_preference_offers: 54,
+    first_preference_offer_pct: 60,
+    oversubscribed: true,
+    ...overrides,
+  };
+}
+
+const census: SchoolCensus = {
+  year: 2024,
+  total_pupils: 420,
+  female_pupils: 205,
+  male_pupils: 215,
+  fsm_pct: 18.4,
+  eal_pct: 22.1,
+};
+
+const absence: AbsenceData = {
+  overall_absence_rate: 5.2,
+  persistent_absence_rate: 14.8,
+};
+
+const deprivation: SchoolDeprivation = {
+  lsoa_code: 'E01000001',
+  idaci_score: 0.21,
+  idaci_decile: 4,
+};
+
+const finance: SchoolFinance = {
+  year: 2024,
+  per_pupil_spend: 5400,
+  staff_cost_pct: 72.5,
+  teacher_cost_pct: 51.2,
+  support_staff_cost_pct: 21.3,
+  premises_cost_pct: 6.1,
+};
+
+// ---------------------------------------------------------------------------
+// National averages
+// ---------------------------------------------------------------------------
+
+export const nationalAveragesFixture: NationalAverages = {
+  year: 2024,
+  primary: { rwm_expected_pct: 61, rwm_high_pct: 8, reading_expected_pct: 74 },
+  secondary: { attainment_8_score: 45.9, progress_8_score: 0, ebacc_entry_pct: 39 },
+  by_year: [
+    { year: 2023, primary: { rwm_expected_pct: 60 }, secondary: { attainment_8_score: 44.4 } },
+    { year: 2024, primary: { rwm_expected_pct: 61 }, secondary: { attainment_8_score: 45.9 } },
+  ],
+};
+
+// ---------------------------------------------------------------------------
+// Fixture 1: ordinary primary — KS2 results, legacy OEIF, 3 admissions years
+// ---------------------------------------------------------------------------
+
+export const primaryFixture = {
+  schoolInfo: makeSchool(),
+  yearlyData: [
+    makeResult({ year: 2022, rwm_expected_pct: 54, reading_expected_pct: 68, writing_expected_pct: 62, maths_expected_pct: 65, total_pupils: 58 }),
+    makeResult({ year: 2023, rwm_expected_pct: 56, reading_expected_pct: 70, writing_expected_pct: 64, maths_expected_pct: 67, total_pupils: 60 }),
+    makeResult({
+      year: 2024,
+      rwm_expected_pct: 58, rwm_high_pct: 9,
+      reading_expected_pct: 72, writing_expected_pct: 66, maths_expected_pct: 69,
+      reading_progress: 0.4, writing_progress: -0.2, maths_progress: 1.1,
+      disadvantaged_pct: 24.5, eal_pct: 22.1, sen_support_pct: 13.2,
+      total_pupils: 60,
+    }),
+  ],
+  absenceData: absence,
+  ofsted: makeOfsted({
+    framework: 'OEIF',
+    inspection_date: '2023-05-17',
+    inspection_type: 'Section 5',
+    overall_effectiveness: 2,
+    quality_of_education: 2,
+    behaviour_attitudes: 1,
+    personal_development: 2,
+    leadership_management: 2,
+    previous_overall: 3,
+    grade_source: 'graded',
+  }),
+  census,
+  admissions: makeAdmissions({ year: 2024 }),
+  admissionsHistory: [
+    makeAdmissions({ year: 2022, first_preference_offer_pct: 71 }),
+    makeAdmissions({ year: 2023, first_preference_offer_pct: 65 }),
+    makeAdmissions({ year: 2024, first_preference_offer_pct: 60 }),
+  ],
+  deprivation,
+  finance,
+};
+
+// ---------------------------------------------------------------------------
+// Fixture 2: secondary — KS4 results, Report Card Ofsted, single admissions year
+// ---------------------------------------------------------------------------
+
+export const secondaryFixture = {
+  schoolInfo: makeSchool({
+    urn: 234567,
+    school_name: 'Test Secondary School',
+    phase: 'Secondary',
+    age_range: '11-16',
+    school_type: 'Academy converter',
+    school_type_code: 'AC',
+  }),
+  yearlyData: [
+    makeResult({ year: 2023, attainment_8_score: 44.8, progress_8_score: 0.18 }),
+    makeResult({
+      year: 2024,
+      attainment_8_score: 46.2, progress_8_score: 0.31,
+      progress_8_banding: 'Above average',
+      english_maths_standard_pass_pct: 68.4,
+      english_maths_strong_pass_pct: 47.1,
+      ebacc_entry_pct: 41.2, ebacc_standard_pass_pct: 28.6,
+      ebacc_strong_pass_pct: 19.4, ebacc_avg_score: 4.31,
+      disadvantaged_pct: 27.8, eal_pct: 19.3, sen_support_pct: 11.7,
+    }),
+  ],
+  absenceData: absence,
+  ofsted: makeOfsted({
+    framework: 'ReportCard',
+    inspection_date: '2025-11-20',
+    rc_inspection_date: '2025-11-20',
+    rc_safeguarding_met: true,
+    rc_inclusion: 2,
+    rc_curriculum_teaching: 2,
+    rc_achievement: 3,
+    rc_attendance_behaviour: 2,
+    rc_personal_development: 1,
+    rc_leadership_governance: 2,
+  }),
+  census,
+  admissions: makeAdmissions({ year: 2024, school_phase: 'Secondary' }),
+  admissionsHistory: [makeAdmissions({ year: 2024, school_phase: 'Secondary' })],
+  deprivation,
+  finance,
+};
+
+// ---------------------------------------------------------------------------
+// Fixture 3: all-through — BOTH key stages on the same row.
+// The highest-value fixture: isAllThrough gates the KS2 content back on for a
+// school that also has KS4 data, and this is the case most likely to break.
+// ---------------------------------------------------------------------------
+
+export const allThroughFixture = {
+  schoolInfo: makeSchool({
+    urn: 345678,
+    school_name: 'Test All-Through School',
+    phase: 'All-through',
+    age_range: '4-18',
+    has_sixth_form: true,
+  }),
+  yearlyData: [
+    makeResult({ year: 2023, rwm_expected_pct: 55, attainment_8_score: 45.0 }),
+    makeResult({
+      year: 2024,
+      rwm_expected_pct: 63, reading_expected_pct: 76,
+      writing_expected_pct: 70, maths_expected_pct: 71,
+      attainment_8_score: 48.7, progress_8_score: 0.42,
+      english_maths_standard_pass_pct: 71.2,
+      disadvantaged_pct: 20.1, eal_pct: 17.5, sen_support_pct: 9.8,
+    }),
+  ],
+  absenceData: absence,
+  ofsted: makeOfsted({
+    framework: 'OEIF',
+    inspection_date: '2022-10-04',
+    inspection_type: 'Section 5',
+    overall_effectiveness: 1,
+    quality_of_education: 1,
+    behaviour_attitudes: 1,
+    personal_development: 1,
+    leadership_management: 1,
+    grade_source: 'graded',
+  }),
+  census,
+  admissions: makeAdmissions({ year: 2024, school_phase: 'Secondary' }),
+  admissionsHistory: [
+    makeAdmissions({ year: 2023, school_phase: 'Secondary', first_preference_offer_pct: 58 }),
+    makeAdmissions({ year: 2024, school_phase: 'Secondary', first_preference_offer_pct: 52 }),
+  ],
+  deprivation,
+  finance,
+};
+
+// ---------------------------------------------------------------------------
+// Fixture 4: special school — all-zero KS2 row.
+// Guards the PR #70 regression: special/PRU/AP schools must not be shown an
+// England comparison, because their pupils sit the same tests but very few
+// reach the mainstream "expected standard".
+// ---------------------------------------------------------------------------
+
+export const specialFixture = {
+  schoolInfo: makeSchool({
+    urn: 456789,
+    school_name: 'Test Special School',
+    school_type: 'Community special school',
+    school_type_code: 'CYS',
+    age_range: '2-19',
+  }),
+  yearlyData: [
+    makeResult({
+      year: 2024,
+      rwm_expected_pct: 0,
+      reading_expected_pct: 0,
+      writing_expected_pct: 0,
+      maths_expected_pct: 0,
+      total_pupils: 12,
+    }),
+  ],
+  absenceData: absence,
+  ofsted: null,
+  census,
+  admissions: null,
+  admissionsHistory: [],
+  deprivation,
+  finance,
+};
diff --git a/nextjs-app/jest.setup.js b/nextjs-app/jest.setup.js
index 46662f2..256811b 100644
--- a/nextjs-app/jest.setup.js
+++ b/nextjs-app/jest.setup.js
@@ -27,6 +27,23 @@ Object.defineProperty(window, 'matchMedia', {
   })),
 });
 
+// jsdom implements neither of these; the school detail views use both
+// (IntersectionObserver for the scroll-spy and the hero-CTA tracker,
+// scrollTo for the "back to top" control).
+global.IntersectionObserver = class {
+  constructor(callback) {
+    this.callback = callback;
+  }
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+  takeRecords() {
+    return [];
+  }
+};
+
+window.scrollTo = jest.fn();
+
 // Mock localStorage
 const localStorageMock = {
   getItem: jest.fn(),