school_compare/docs/superpowers/specs/2026-09-21-similar-schools-nearby-design.md

Other Schools Nearby — Design

Date: 2026-09-21, revised 2026-09-22 Status: revised after staging review Scope: school detail pages, both phase templates

Revision, 2026-09-22. The first build ranked by intake similarity and used distance as a tiebreak. On staging a Catholic primary showed six Catholic primaries, none of them close enough to be a real option, and omitted the community school down the road. Distance now decides the order and nothing else does; the tier system is gone. The reasoning is kept below rather than quietly overwritten, because the mistake is the instructive part.

Goal

Give a school detail page an answer to the question every reader arrives with after the results tables: and what else is around here?

Today a school page links outward to its place pages through components/school/NearbyPlaces.tsx and nowhere else. It never links to another school. This section adds that edge — up to six nearby schools of the same phase and a comparable intake, three at a time in a carousel, each a crawlable link and each addable to the comparison basket in one click.

Mockup, in both themes (drawn against the original tiered design, so its ledes and chip fallbacks are one revision behind the copy specified below): https://claude.ai/artifact/168KdUMcfkUeGWW2FGjuec

Source of the same page in the repo: mockups/similar-schools-nearby.html.

The constraint that shapes everything

A nearby school is not automatically a comparable school.

The section's whole value is that a reader treats what it shows as a shortlist. That makes every card an implicit claim that the school is a realistic alternative, and there are three ways that claim goes wrong:

1. A selective school beside a non-selective one. Their intakes are different by construction, so putting their Attainment 8 figures side by side invites a conclusion the data cannot support.
2. A special school, PRU or AP beside a mainstream school. This is the same error PR #70 fixed for the England benchmark, where Greenmead (URN 101099) rendered "0% — 62 below England".
3. A single-sex school of the opposite sex. Not a weak match — not an option at all.

So the design separates two kinds of fact, and never confuses them:

• Hard filters encode the claims above. They decide eligibility, and are never relaxed at any distance, even if that means the section does not render.
• Shared characteristics — gender, religious character, selectivity — describe how closely an intake resembles this school's. They are reported on the card and never ranked on, so the reader weighs them rather than having them weighed for them.

Everything below follows from that split. The revision at the top of this document is what happens when the second kind is treated as the first.

Selection algorithm

A backend helper, _nearby_schools_payload(urn) in backend/app.py, modelled on the existing _places_payload(urn) and delegating to backend/nearby_schools.select_nearby(frame, urn), which operates on the cached load_latest_school_data() frame — one row per URN, already carrying latitude, longitude, phase, gender, religious_denomination, admissions_policy, school_type and status.

Hard filters

Filter	Rule
Self	urn is excluded
Status	GIAS status must be open
Coordinates	both latitude and longitude present on both schools
Phase	same phase group via the existing PHASE_GROUPS map
Provision	special/PRU/AP match only each other
Selectivity	selective matches selective; non-selective matches non-selective
Gender	Boys never matches Girls; Mixed is compatible with both

PHASE_GROUPS is reused rather than re-derived so an all-through school is offered correctly on both the primary and secondary sides, exactly as it already behaves in search.

The provision filter needs a backend counterpart to the frontend's isSpecialSchool() in nextjs-app/lib/utils.ts:897, reading the same GIAS establishment types through backend/gias_codes.py. The two must agree: a school the frontend treats as special for benchmarking but the backend treats as mainstream for matching would be dropped from its own England comparison and then offered as a peer to a mainstream school on the next page along.

Up to six cards, three visible. Three fit the row; the rest are reached with the carousel arrows. Two is the minimum that renders at all.

Order: distance, and nothing else

The nearest eligible schools, closest first. Similarity does not enter the ranking at any point.

Why not, having built it the other way first. The original design ranked by tiers — same gender and faith within 3 miles, then same gender within 5, then anything within 10 — and used distance only to order the result. Two things followed, and both showed up on the first Catholic primary anyone looked at:

• A faith match at 2.9 miles outranked a community school at 0.3 miles. For a primary, whose catchment is routinely under a mile, the far school is not a weaker option; it is not an option.
• Because the row filled from the best tier before widening, three Catholic schools within 3 miles were enough to fill all six slots with Catholic schools. The stopping rule that produced this had been added to prevent the opposite failure — padding a row with weak distant matches — and made this one certain.

The premise was backwards. Distance is a constraint and intake is a preference. A parent cannot act on a school outside their reach however well it matches, and they are perfectly capable of noticing a shared denomination for themselves if we show it to them. So similarity moved from the ranking to the card: shared reports what a school genuinely has in common, and the reader applies their own weighting.

The hard filters above were always where the defensibility lived. They are untouched.

Reach: a sanity bound, not a target

Phase	Reach
Primary, middle deemed primary, all-through	2 miles
Secondary, middle deemed secondary	6 miles
16 plus	10 miles

Ordering by distance already handles density — a school in inner London fills all six slots inside a mile and never approaches the cap. The cap decides one thing: what happens where the area is sparse. It differs by phase because catchments do, and because people travel furthest for post-16.

A primary with nothing inside two miles renders no section, and that is the intended answer rather than a gap. The alternative is a section headed "nearby" listing a school four miles from a five-year-old.

Past the sixth school, the rest are dropped without a count. The section does not try to be the list: NearbyPlaces sits directly beneath and already leads to the place pages, which are built for browsing a full set and which the school page exists to feed.

Fewer than two results renders nothing. Not an empty state, not a single lonely card. The section is absent, the nav item is absent, and the page is unchanged from before it existed.

Distance

Straight-line, from the vectorised haversine already used for postcode search at backend/app.py:831, computed over the ~27k-row frame in numpy. Reported to one decimal place in miles, consistent with the rest of the site.

Straight-line distance is not road distance and is not measured from the reader's home. The section says so in its disclosure rather than leaving the reader to assume otherwise.

API

/api/schools/{urn} gains a similar_schools array. Each row:

Field	Notes
urn	for the link and the compare basket
school_name	link text
distance_miles	one decimal place
school_type	GIAS type, translated, for the card's meta line
age_range	for the meta line
shared	what this school genuinely shares with the subject; may be empty
metric_value	the phase-appropriate headline figure, or null
metric_key	rwm_expected_pct or attainment_8_score — see below
metric_year	the year the figure is from

The metric follows the subject school's phase side, not the neighbour's own phase, so a row of cards never mixes two scales. The secondary side uses attainment_8_score; the primary side uses rwm_expected_pct. Where the neighbour has no value for that key, the card reads "Not published" rather than falling back to the other key.

Which side a school takes is decided once, in similar_schools.is_secondary_phase, by membership of PHASE_GROUPS["secondary"] minus all-through — never by testing for the substring "secondary", which misses 16 plus (GIAS phase 6) and hands a sixth-form college the primary bucket. All-through is the exception in the other direction: PHASE_GROUPS lists it on both sides, but it takes the primary metric.

This is usually the same thing as "the template the page renders", but not always. computeSchoolFlags decides the template with that same substring test, so a 16 plus school renders PrimarySchoolSections while being matched — correctly — against secondaries. The section therefore takes its lede noun from the school's own phase rather than from its template, or it would print "Other primary schools near " above a row of secondaries.

Up to six rows of roughly 130 bytes each. It rides in the existing detail payload rather than a new endpoint because the page already makes exactly one server fetch for its data, and /school/[slug] regenerates at most weekly (revalidate = 604800), so the per-request cost is paid once per school per week.

The key is absent, not null, on a backend that does not have this code. The frontend treats absent and empty identically, which is what allowed NearbyPlaces to ship without a lockstep deploy of the two images.

shared is computed on the backend, beside the data it is derived from, not re-derived on the frontend. Deriving it twice is how a card comes to claim something the selection never established. An empty list is a real answer and renders no chips: a bare card costs a school nothing but the likeness it does not have, since the order was already settled by distance.

Frontend

Components

components/school/SimilarSchoolsSection.tsx — a server component wrapped in the shared Section shell from sectionShared.tsx. It renders the heading, the lede, the card grid, the footer CTA and one caption line. Every card's title is an <a> to the school's canonical slug URL via schoolUrl().

components/school/AddToCompareButton.tsx — calls addSchool from ComparisonProvider and reports the selection with a from: 'similar_schools' attribution, mirroring addSchoolFromSearch in HomeView.tsx:442.

components/school/SimilarSchoolsCarousel.tsx — the scroller and its arrows. It takes the server-rendered cards as children and the server-rendered heading and lede as a header prop, so those stay server components while the client component owns only the ref, the scroll handler and the arrows' disabled state.

The split matters: the links — the part with SEO value and the part that must work without JavaScript — are server-rendered into the initial HTML, and only the basket interaction and the arrows are hydrated.

The carousel

Every card is in the initial HTML. The arrows scroll a list; they never swap a view. Six <a> elements are in the markup whether or not anything is hydrated, which is the whole reason the section exists — a paginated widget that mounts cards on click would put four of the six links beyond a crawler and beyond a reader with no JavaScript.

So the scroller is a plain overflowing <ul> with scroll-snap-type: x mandatory, and the arrows call scrollBy on it. With no JavaScript it degrades to a horizontally scrollable row that still works by touch and by trackpad. Three cards are visible at desktop width and two below 820px.

Arrows appear only when there is somewhere to go — that is, only when more than three schools were found. Each disables itself at its own end of the travel.

Below 640px the arrows go away

This follows MOBILE.md, which makes 360px the design floor and mobile the primary target at ≥55% of traffic.

Kept in the heading's flex row at 360px, the two arrow buttons take 96px from a 328px card and crush the lede into a four-line column — measured, not guessed. And swiping already does what they do. So below 640px the header becomes a single column, the arrows are not rendered, one card shows at 86% width so the next one peeks, and the affordance is carried by the right-edge scroll-fade that MOBILE.md documents for exactly this case:

mask-image: linear-gradient(to right, #000 calc(100% - 28px), transparent);

The fade lifts at the end of the travel, where there is nothing left to hint at. That means the at-end state must be computed whether or not an arrow exists to consume it — on mobile it drives the mask alone.

Every interactive element clears 44×44px, per MOBILE.md's iOS HIG check: the arrow buttons and the add-to-compare button are both 44px, up from the 40px they were first drawn at. A card title's own box is shorter than that, but its hit area is the whole card through the ::after overlay, so it passes on the target that actually receives the tap.

The edge test needs a tolerance, and this is not fussiness. The scroller carries 2px of padding so focus rings are not clipped, and scroll-snap treats that padding as the first card's snap position: a scroller sitting at its start reports scrollLeft of 2, not 0. Sub-pixel rounding moves it again at other zoom levels. Testing scrollLeft === 0 therefore leaves the back arrow live and pointing nowhere on first paint — confirmed in the mockup before it was fixed. Both ends compare against an 8px tolerance.

Selecting a school must not move the row. Adding to the basket re-renders the footer; the scroll offset lives in the DOM rather than in React state, so the carousel must not remount or reset on that render. A reader who ticks the fifth school and is thrown back to the first has been punished for using the feature.

Placement and navigation

Rendered as the last section inside SchoolDetailShell, from both PrimarySchoolSections and SecondarySchoolSections. Inside, not after, because the sticky nav's scroll-spy locates sections with document.getElementById and can only reach a section that lives in the shell.

NearbyPlaces stays where it is, outside the shell, immediately below. The resulting order — this school, then similar schools, then the places containing them — narrows before it widens, which is the order a reader leaves a page in.

buildNavItems and buildSecondaryNavItems both gain { id: 'similar', label: 'Similar schools' }, gated on the section rendering. The id must match the Section id or the scroll-spy silently breaks.

The comparison CTA

A plain <a href="/compare?urns=…">, built from this school's URN plus the selected ones. /compare already parses urns from the query string (app/(frontend)/compare/page.tsx:55), so this needs no new compare plumbing. With nothing selected the CTA is disabled; the button also adds to the shared basket so the site-wide comparison state stays consistent with what the page shows.

Copy, and what the section is allowed to claim

The lede never claims an intake. It reads "Other primary schools near X." — one sentence, no variants. The earlier version varied the wording by tier, which only existed to soften a claim the section should not have been making.

The heading is "Other schools nearby", not "Similar schools nearby". The hard filters do guarantee a comparable set — same phase, same selectivity, mainstream never beside special — but nothing ranks on likeness, so the heading does not say it does. The nav item reads "Nearby schools" and the section id is nearby.

Chips state only what is shared, and may be absent entirely. A card with nothing in common renders no chip row rather than falling back to a filler. Since chips no longer affect the order, an empty one costs that school nothing except a claim it cannot support — and a Catholic parent scanning the row still spots "Roman Catholic" on the card that carries it, and weighs it themselves.

The neighbour's metric carries no valence colour. Green and terracotta are reserved site-wide for comparison against the England average. Colouring a neighbour's figure against this school's would read as ranking the neighbours against each other, which is precisely the endorsement this section must not make. The figure sits in neutral ink above a plain "72% at this school" reference line, and the reader draws their own conclusion.

A missing figure reads "Not published". Never 0, never blank, never an em dash. This follows the same rule the rest of the detail page uses: a school with no published result has not scored zero.

There is no "how these are chosen" disclosure. The method is visible in what the section already shows — the phase in the lede, the shared characteristics on each card, the distance above each name — and a collapsed panel restating it earns less than the space it costs.

One caption line survives, and only one: that distances are straight-line from the school and not road distance. This is not a method note. A reader who sees "0.6 miles away" and takes it for the walk has been misled by us, and no other element on the card corrects that. The remaining notes — that listing is not a recommendation, that special schools only meet special schools — are statements the selection rules already keep true without being narrated.

Degradation

Condition	Behaviour
similar_schools absent (older backend image)	no section, no nav item
fewer than 2 qualifying schools	no section, no nav item
this school has no coordinates	no section
the helper raises	returns []; the page renders without the section

The helper is wrapped so a failure inside it never 500s a page that is otherwise complete — the posture get_supplementary_data already takes for its own queries.

Testing

Backend, in a new backend/tests/test_similar_schools.py, against a synthetic frame rather than live marts:

• a selective school never returns a non-selective one, and vice versa
• a special school returns only special schools; a mainstream school returns none
• a Boys school never returns a Girls school; Mixed matches both
• closed schools and schools without coordinates are never returned
• results are ordered by distance ascending, always
• a faith match never outranks a closer school (the staging defect, pinned)
• the nearest eligible school is always present
• more than six qualifying schools returns the six nearest
• reach is capped per phase, and a primary beyond two miles returns []
• an all-through school is offered on both phase sides
• a 16 plus school is matched against secondaries and colleges, never primaries
• is_secondary_phase and PHASE_GROUPS agree on every GIAS phase value
• fewer than two qualifying schools returns []
• distances match a hand-computed haversine for a known pair

Frontend, in nextjs-app/__tests__:

• the section renders nothing for absent, empty and single-row inputs
• the lede never claims a similar intake
• an empty shared renders no chips rather than a filler
• a null metric renders "Not published"
• the nav item appears only alongside the section
• every card is in the DOM, including the ones scrolled out of view
• arrows render only when more than three schools were found

jsdom has no layout, so scrollWidth and clientWidth are both 0 there and the arrows' disabled state cannot be meaningfully asserted in Jest. That behaviour is covered in the journey instead, against a real engine, rather than by a unit test that would pass on a measurement that does not exist.

E2E, added to the existing journeys in e2e/tests in the same PR, per the repository's rule on user-facing behaviour:

• the section renders on a known staging URN, with resolving links
• where arrows are present, the back arrow starts disabled and the forward arrow moves the row
• selecting a school does not reset the scroll position
• add-to-compare reaches /compare with the expected urns
• at 360, 390 and 430px: no horizontal overflow, every interactive element in the section clears 44×44px, and no arrows are rendered

The E2E gate runs after merge on this project, so these journeys are not provable in the PR checks; the PR is verified on the unit tests, and the journeys are confirmed on the post-merge staging run.

Out of scope

• A map of the nearby schools. The section is a list; the page already has a map.
• Autoplay, dots, or an infinite loop on the carousel. It is a short list a reader scans deliberately, not a banner competing for attention, and a row that moves on its own is a row that moves while someone is reading it.
• Statistical neighbours on deprivation, size or cohort profile. If plain distance proves too blunt, that is the trigger to move this computation into a dbt mart — select_nearby is a deliberate seam for exactly that swap.
• Precomputing neighbours in marts.*. Rejected for now: a new mart is inert until Airflow runs, so the feature would ship dark, and every tuning change to the rules would become a pipeline round-trip instead of a deploy. The revision at the top of this document is the argument for keeping that loop short.
• Any change to /api/compare, the compare page, or the comparison basket.