GeraLearn / School Resource Index / Methodology
Gera School Resource Index — Methodology
How the GSRI is computed, what data it uses, and how you can verify every number independently.
How is the Gera School Resource Index (GSRI) calculated?
The Gera School Resource Index (GSRI) uses two real DfE figures for each local authority: average primary class size and average secondary class size (2025/26). pScore = round((26.16 ÷ la_primary) × 100, 1); sScore = round((22.64 ÷ la_secondary) × 100, 1); GSRI = round((pScore + sScore) ÷ 2, 1). England mean = 100; >100 = smaller classes than average. Source: DfE 2025/26, OGL v3.0.
Full formula
Input variables (per LA):
la_primary= average primary school class size (DfE 2025/26)la_secondary= average secondary school class size (DfE 2025/26)
National baselines (pupil-weighted England averages):
nat_primary= 26.16 (computed from 3,974,132 primary pupils across 152 published LAs)nat_secondary= 22.64 (computed from 3,359,927 secondary pupils across 152 published LAs)
Formula:
pScore = round((nat_primary / la_primary) × 100, 1) sScore = round((nat_secondary / la_secondary) × 100, 1) GSRI = round((pScore + sScore) / 2, 1)
Interpretation: GSRI = 100 means exactly at the England average class size. GSRI above 100 = smaller classes than average (more resource per pupil). GSRI below 100 = larger classes. The index is published for 151 LAs with both primary and secondary data; 1 LA with only one phase is omitted (honesty gate — never estimated).
Data source
Publication: DfE — Schools, pupils and their characteristics, Academic year 2025/26
Dataset: “Class sizes - state-funded primary and secondary schools” (Dataset ID: 019e7401-70d1-73ca-9855-bd7258e5a1ca)
API: https://api.education.gov.uk/statistics/v1/data-sets/019e7401-…
Filter applied: geographic_level = Local authority, time_period = 2025/2026, size_of_class = Total, type_of_class = Primary AND Secondary (separate queries merged by LA location ID).
Licence: Open Government Licence v3.0 — content reused under this licence.
As of: Academic year 2025/26 · data retrieved 2026-06-20
Update cadence: Annual (DfE publishes class-size data once per academic year). GeraLearn re-dates GSRI figures annually when the DfE releases updated data.
What the GSRI does and does not measure
Does measure: average primary and secondary class size across state-funded schools in an LA, relative to the England average. A higher GSRI reflects smaller classes on average, which generally means more direct teacher time per pupil.
Does not measure: school quality, teacher qualifications, per-pupil funding levels, school type mix (academies vs LA-maintained), private school provision, or pupil outcomes. Class size is one dimension of resource; other measures are available in the Gera Academic Attainment Index (GCSE outcomes) and Gera School Quality Index (Ofsted grades).
Honesty gate: We omit rather than estimate. No GSRI is published for an LA where DfE did not publish BOTH primary and secondary figures. Cells with <5 classes are normally suppressed by DfE at source.