fix(compare): a no-results school no longer blanks the trend chart

Adding a school with no performance data to a comparison made every
school's trend line disappear until that school was removed.

Root cause: /api/compare returns such a school with a single phantom
yearly_data row (the dim_school LEFT JOIN) whose year is null. In
buildCompareChart, Math.trunc(null) is 0, so the axis was seeded at
year 0; fillAcademicYears then walked 0, 101, 202, … and hit its
50-step cap long before reaching the real years, leaving every
school's series mapped entirely to null.

Fix: ignore yearly rows without a real numeric year when building the
axis and the per-school year map. Regression test added.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app.py

@@ -807,6 +807,10 @@ async def get_la_averages(request: Request):
 _KS2_NATIONAL_METRICS = [
     "rwm_expected_pct", "rwm_high_pct",
     "reading_expected_pct", "writing_expected_pct", "maths_expected_pct",
+    # Per-subject higher-standard nationals: reading/maths reach the "higher
+    # standard" in the tests; writing is teacher-assessed at "greater depth"
+    # (writing_gd_pct). Needed so each SATs bar compares to its own benchmark.
+    "reading_high_pct", "writing_gd_pct", "maths_high_pct",
     "gps_expected_pct", "gps_high_pct", "science_expected_pct",
     "reading_avg_score", "maths_avg_score", "gps_avg_score",
     "reading_progress", "writing_progress", "maths_progress",

backend/tests/test_national_averages_marts.py

@@ -25,6 +25,11 @@ class _Ks2Row:
     year = LATEST
     rwm_expected_pct = 62.1
     gps_expected_pct = 72.0
+    # Per-subject higher-standard nationals — reading/maths reach the higher
+    # standard, writing is teacher-assessed at greater depth (writing_gd_pct).
+    reading_high_pct = 29.0
+    writing_gd_pct = 13.0
+    maths_high_pct = 24.0
 
 
 class _Ks4Row:
@@ -84,6 +89,16 @@ def test_ks4_averages_come_from_the_mart_not_the_dataframe(payload):
     assert body["by_year"][-1]["secondary"]["progress_8_score"] == -0.02
 
 
+def test_per_subject_higher_standard_nationals_are_surfaced(payload):
+    # The SATs chart compares each bar to its own benchmark, so the per-subject
+    # higher-standard / greater-depth nationals must reach the payload — not
+    # only the combined rwm_high_pct.
+    body = payload(_StubSession)
+    assert body["primary"]["reading_high_pct"] == 29.0
+    assert body["primary"]["writing_gd_pct"] == 13.0
+    assert body["primary"]["maths_high_pct"] == 24.0
+
+
 def test_ks4_secondary_empty_when_mart_missing(payload):
     # No computed stand-in: the UI labels national figures as official DfE
     # data, so an empty mart must yield an empty secondary series.

nextjs-app/__tests__/lib/compareChartData.test.ts

@@ -41,6 +41,30 @@ describe('buildCompareChart', () => {
     }
   });
 
+  it('ignores a no-results school whose only row has a null year', () => {
+    // A school with no performance rows comes back from /api/compare with a
+    // single phantom yearly_data row (LEFT JOIN) where year and every metric
+    // are null. That null year must NOT pollute the axis: Math.trunc(null) is
+    // 0, and filling from year 0 blows past the real years, blanking every
+    // school's line. Regression guard for "add a no-data school → chart empty".
+    const withNoData = {
+      ...THREE_SCHOOLS,
+      '4': school(4, [[null as unknown as number, null]]),
+    };
+    const list = [...SCHOOL_LIST, { urn: 4, school_name: 'School 4' }];
+    const chart = buildCompareChart(withNoData, list, 'rwm_expected_pct');
+
+    // The real years still drive the axis; the phantom year 0 is gone.
+    expect(chart.years).toContain(201819);
+    expect(chart.years).toContain(202425);
+    expect(chart.years).not.toContain(0);
+    // The three real schools still render their lines.
+    for (const urn of [1, 2, 3]) {
+      const ds = chart.schoolDatasets[urn - 1];
+      expect(ds.data.some((v) => v != null)).toBe(true);
+    }
+  });
+
   it('handles float years from the API (202425.0 style)', () => {
     const floaty = {
       '1': school(1, [[201819.0 as number, 80], [202425.0 as number, 85]]),

nextjs-app/app/layout.tsx

@@ -85,6 +85,14 @@ export default function RootLayout({
           data-performance="true"
           strategy="afterInteractive"
         />
+        {/* Heatmap / session recorder — same data-domains guard so staging
+            (same image, different host) never feeds the heatmap. */}
+        <Script
+          src="https://analytics.schoolcompare.co.uk/recorder.js"
+          data-website-id="d7fb0c95-bb6c-4336-8209-bd10077e50dd"
+          data-domains="schoolcompare.co.uk,www.schoolcompare.co.uk"
+          strategy="afterInteractive"
+        />
       </head>
       <body className={`${dmSans.variable} ${playfairDisplay.variable}`}>
         <div className="noise-overlay" />

nextjs-app/components/SatsChart.module.css

@@ -44,30 +44,46 @@
   background: var(--bg-secondary, #f3ede4);
 }
 
-/* ── National average marker ── */
+/* ── Per-bar national average marker ──
-.natLine {
+   Each bar compares against its own benchmark (expected vs higher standard /
+   greater depth), so the marker sits on the individual bar's track rather than
+   as one line spanning both bars. */
+.natTick {
   position: absolute;
-  top: 0;
+  top: -3px;
-  height: calc(100% - 20px);
+  bottom: -3px;
-  width: 1.5px;
+  width: 2px;
-  background: rgba(224, 114, 86, 0.35); /* --accent-coral at 35% */
+  transform: translateX(-50%);
-  z-index: 2;
+  background: var(--accent-coral, #e07256);
+  border-radius: 2px;
+  z-index: 4;
   pointer-events: none;
 }
 
-.natPill {
+.natTick::before {
+  content: '';
   position: absolute;
-  top: -10px;
+  top: -3px;
+  left: 50%;
   transform: translateX(-50%);
+  width: 5px;
+  height: 5px;
+  border-radius: 50%;
   background: var(--accent-coral, #e07256);
-  color: #fff;
+}
+
+.barHeaderRight {
+  display: flex;
+  align-items: baseline;
+  gap: 0.4rem;
+}
+
+.natLabel {
   font-size: 0.55rem;
   font-weight: 700;
-  padding: 0.1rem 0.35rem;
+  color: var(--accent-coral-dark, #b04a2e);
-  border-radius: 4px;
+  text-transform: uppercase;
-  white-space: nowrap;
+  letter-spacing: 0.03em;
-  z-index: 3;
-  letter-spacing: 0.02em;
 }
 
 /* ── Bar rows ── */

nextjs-app/components/SatsChart.tsx

@@ -8,6 +8,9 @@ interface SubjectData {
   expectedPct: number | null;
   exceedingPct: number | null;
   nationalExpectedPct: number | null;
+  /** National higher-standard / greater-depth benchmark for the exceeding
+   * bar — a different figure from the expected national. */
+  nationalExceedingPct: number | null;
 }
 
 interface SatsChartProps {
@@ -17,11 +20,45 @@ interface SatsChartProps {
 const RULER_TICKS = [0, 25, 50, 75, 100];
 const GRIDLINE_POSITIONS = [25, 50, 75];
 
+/** One results bar with a national marker positioned on its own track, so the
+ * expected and exceeding bars each compare against their own benchmark. */
+function BarRow({
+  label,
+  value,
+  national,
+  barRef,
+  barClass,
+}: {
+  label: string;
+  value: number;
+  national: number | null;
+  barRef: React.RefObject<HTMLDivElement | null>;
+  barClass: string;
+}) {
+  return (
+    <div className={styles.barRow}>
+      <div className={styles.barHeader}>
+        <span className={styles.barLabelSuffix}>{label}</span>
+        <span className={styles.barHeaderRight}>
+          {national != null && <span className={styles.natLabel}>nat {national.toFixed(0)}%</span>}
+          <span className={styles.barLabel}>{value.toFixed(0)}%</span>
+        </span>
+      </div>
+      <div className={styles.barTrack}>
+        <div ref={barRef} className={`${styles.bar} ${barClass}`} data-width={value} />
+        {national != null && (
+          <div className={styles.natTick} style={{ left: `${national}%` }} aria-hidden="true" />
+        )}
+      </div>
+    </div>
+  );
+}
+
 function SubjectColumn({ subject }: { subject: SubjectData }) {
   const expectedRef = useRef<HTMLDivElement>(null);
   const exceedingRef = useRef<HTMLDivElement>(null);
 
-  const { name, expectedPct, exceedingPct, nationalExpectedPct } = subject;
+  const { name, expectedPct, exceedingPct, nationalExpectedPct, nationalExceedingPct } = subject;
 
   // Animate bars on mount
   useEffect(() => {
@@ -51,44 +88,25 @@ function SubjectColumn({ subject }: { subject: SubjectData }) {
           ))}
         </div>
 
-        {/* National average marker */}
+        {/* Bars — each carries its own national marker */}
-        {nationalExpectedPct != null && (
-          <div className={styles.natLine} style={{ left: `${nationalExpectedPct}%` }}>
-            <div className={styles.natPill}>{nationalExpectedPct.toFixed(0)}%</div>
-          </div>
-        )}
-
-        {/* Bars */}
         <div className={styles.barGroup}>
           {expectedPct != null && (
-            <div className={styles.barRow}>
+            <BarRow
-              <div className={styles.barHeader}>
+              label="Expected"
-                <span className={styles.barLabelSuffix}>Expected</span>
+              value={expectedPct}
-                <span className={styles.barLabel}>{expectedPct.toFixed(0)}%</span>
+              national={nationalExpectedPct}
-              </div>
+              barRef={expectedRef}
-              <div className={styles.barTrack}>
+              barClass={styles.barExpected}
-                <div
-                  ref={expectedRef}
-                  className={`${styles.bar} ${styles.barExpected}`}
-                  data-width={expectedPct}
             />
-              </div>
-            </div>
           )}
           {exceedingPct != null && (
-            <div className={styles.barRow}>
+            <BarRow
-              <div className={styles.barHeader}>
+              label="Exceeding"
-                <span className={styles.barLabelSuffix}>Exceeding</span>
+              value={exceedingPct}
-                <span className={styles.barLabel}>{exceedingPct.toFixed(0)}%</span>
+              national={nationalExceedingPct}
-              </div>
+              barRef={exceedingRef}
-              <div className={styles.barTrack}>
+              barClass={styles.barExceeding}
-                <div
-                  ref={exceedingRef}
-                  className={`${styles.bar} ${styles.barExceeding}`}
-                  data-width={exceedingPct}
             />
-              </div>
-            </div>
           )}
         </div>
 
@@ -135,7 +153,7 @@ export default function SatsChart({ subjects }: SatsChartProps) {
           Exceeding / high score
         </div>
         <div className={styles.legendItem}>
-          <div className={styles.legendSwatch} style={{ background: 'var(--accent-coral, #e07256)', borderRadius: '50%' }} />
+          <div className={styles.legendSwatch} style={{ background: 'var(--accent-coral, #e07256)', width: '3px', height: '12px', borderRadius: '2px' }} />
           National average
         </div>
       </div>

nextjs-app/components/SchoolDetailView.module.css

@@ -855,7 +855,10 @@
 /* Charts Section */
 .chartContainer {
     width: 100%;
-    height: 280px;
+    /* Taller on desktop so the trend lines have vertical room to separate
+       and read clearly. Mobile overrides this to height:auto below (the
+       max-width:768px query), so this only affects desktop. */
+    height: 380px;
     position: relative;
 }
 

nextjs-app/components/SchoolDetailView.tsx

@@ -752,18 +752,22 @@ export function SchoolDetailView({
                       expectedPct: latestResults.reading_expected_pct,
                       exceedingPct: latestResults.reading_high_pct,
                       nationalExpectedPct: suppressKs2Comparison ? null : primaryAvg.reading_expected_pct,
+                      nationalExceedingPct: suppressKs2Comparison ? null : primaryAvg.reading_high_pct,
                     },
                     {
                       name: 'Writing',
                       expectedPct: latestResults.writing_expected_pct,
                       exceedingPct: latestResults.writing_high_pct,
                       nationalExpectedPct: suppressKs2Comparison ? null : primaryAvg.writing_expected_pct,
+                      // Writing's higher level is teacher-assessed "greater depth".
+                      nationalExceedingPct: suppressKs2Comparison ? null : primaryAvg.writing_gd_pct,
                     },
                     {
                       name: 'Maths',
                       expectedPct: latestResults.maths_expected_pct,
                       exceedingPct: latestResults.maths_high_pct,
                       nationalExpectedPct: suppressKs2Comparison ? null : primaryAvg.maths_expected_pct,
+                      nationalExceedingPct: suppressKs2Comparison ? null : primaryAvg.maths_high_pct,
                     },
                   ]}
                 />

nextjs-app/components/SecondarySchoolDetailView.module.css

@@ -490,7 +490,10 @@
 /* ── Charts & Map ────────────────────────────────────── */
 .chartContainer {
     width: 100%;
-    height: 280px;
+    /* Taller on desktop so the trend lines have vertical room to separate
+       and read clearly. Mobile overrides this to height:auto below (the
+       max-width:768px query), so this only affects desktop. */
+    height: 380px;
     position: relative;
 }
 

nextjs-app/lib/compareChartData.ts

@@ -10,6 +10,17 @@
 
 import type { ComparisonData } from './types';
 
+/**
+ * A yearly row only counts once it carries a real academic year. A school with
+ * no performance data still comes back from /api/compare with a single phantom
+ * row (the dim_school LEFT JOIN) where `year` is null — and Math.trunc(null) is
+ * 0, which would seed the axis at year 0 and, via fillAcademicYears, blow past
+ * every real year and blank all schools' lines. Drop those rows up front.
+ */
+function hasYear(row: { year: number }): boolean {
+  return typeof row.year === 'number' && Number.isFinite(row.year);
+}
+
 /** 201819 → 201920 (academic-year arithmetic on YYYYYY codes). */
 function nextAcademicYear(year: number): number {
   const start = Math.floor(year / 100);
@@ -66,14 +77,19 @@ export function buildCompareChart(
   nationalByYear?: Record<number, number | null | undefined>,
 ): CompareChart {
   const rawYears = schools.flatMap(
-    (s) => comparisonData[String(s.urn)]?.yearly_data.map((d) => Math.trunc(d.year)) ?? [],
+    (s) =>
+      comparisonData[String(s.urn)]?.yearly_data.filter(hasYear).map((d) => Math.trunc(d.year)) ??
+      [],
   );
   const years = fillAcademicYears(rawYears);
 
   const schoolDatasets: CompareChartSeries[] = schools.map((school, schoolIndex) => {
     const rows = comparisonData[String(school.urn)]?.yearly_data ?? [];
     const byYear = new Map<number, Record<string, unknown>>();
-    for (const row of rows) byYear.set(Math.trunc(row.year), row as unknown as Record<string, unknown>);
+    for (const row of rows) {
+      if (!hasYear(row)) continue;
+      byYear.set(Math.trunc(row.year), row as unknown as Record<string, unknown>);
+    }
     return {
       label: school.school_name,
       data: years.map((year) => {