Every school system that measures an attainment gap relies on proxies for disadvantage — and most of those proxies are more fragile than the conclusions built on them. The specific instruments vary: Scotland uses SIMD and free meal entitlement; England uses Pupil Premium eligibility and Free School Meals registration. Both systems face the same fundamental problem: the measures are stale, the registration rates undercount, and the gap we report may not be the gap that exists.
The latest Achievement of Curriculum for Excellence Levels (ACEL) data, published in December 2025, showed that the poverty-related attainment gap in primary schools had reached its lowest recorded level — 19.4 percentage points for literacy and 16.6 for numeracy. This was reported as progress. It may be. But before we accept the headline, it is worth asking a more fundamental question: how confident are we in the instruments we are using to measure the gap in the first place?
The attainment gap conversation is a data conversation — and schools need to get better at using the data they already have before layering on new metrics.
Scotland measures the attainment gap primarily by comparing the educational outcomes of pupils in the most and least deprived areas, using the Scottish Index of Multiple Deprivation (SIMD), and by comparing outcomes for pupils who are registered for free school meals (FME) with those who are not. Both measures are established. Both are widely used. And both have structural limitations that, taken together, mean that the gap Scotland thinks it is measuring may not be the gap that actually exists.
SIMD: an area measure doing an individual job
The Scottish Index of Multiple Deprivation ranks 6,976 small areas — data zones of roughly 700–800 people — from most deprived to least deprived, using 43 indicators across seven domains: income, employment, health, education, access to services, crime, and housing. It is Scotland's standard tool for identifying concentrations of deprivation, and it is a good tool for that purpose. The difficulty arises when it is used as a proxy for individual pupil disadvantage, which is how it functions in the attainment gap measurement.
The first problem is staleness. The current SIMD data is SIMD 2020v2, published in January 2020. As of February 2026, it is more than six years old. In the intervening period, Scotland has experienced a pandemic, a cost-of-living crisis, significant changes in housing costs and patterns, and shifts in local economic conditions that are not reflected in the data. A family that moved into a data zone in 2021 because housing was affordable there — or because they were displaced from a more expensive area — does not appear in the SIMD calculations that were finalised before they arrived. The index is updated roughly every four to five years, which means that at any given point in the cycle, the data being used to target support and measure progress is between one and six years out of date. We are currently at the far end of that cycle.
The second problem is ecological. SIMD is an area-based measure. It tells you about the characteristics of a data zone, not about the characteristics of any individual living in it. The Scottish Government itself states this clearly: 'not every person in a highly deprived area will themselves be experiencing high levels of deprivation.' The reverse is equally true: not every person in an affluent area is affluent. When SIMD is used to measure the attainment gap — comparing outcomes for pupils in SIMD Quintile 1 (most deprived 20% of areas) with those in Quintile 5 (least deprived 20%) — it necessarily misclassifies some pupils in both directions. Disadvantaged pupils living in less deprived areas are counted as non-disadvantaged. Relatively advantaged pupils living in deprived areas are counted as disadvantaged. The net effect is a blurring of the gap: some pupils who should be in the numerator are in the denominator, and vice versa.
The third problem is rural. SIMD data zones in rural areas tend to cover larger geographical areas with more mixed populations. A data zone that includes both a prosperous village and a scatter of isolated, low-income households will produce an average deprivation score that describes neither population accurately. The Scottish Government acknowledges this: SIMD 'is less helpful at identifying the smaller pockets of deprivation found in more rural areas.' Since the attainment gap is measured at the national level using SIMD quintiles, the rural misclassification feeds directly into the national picture — and Scotland has a substantial rural school population whose disadvantage is systematically underrepresented.
SIMD isn't the only measure that hides complexity — the 43% ASN figure tells a similar story of a number that has outgrown its usefulness.
FME: a proxy that leaks
Free meal entitlement has been used for decades as a school-level proxy for deprivation, both in Scotland and across the UK. Croxford's analysis of FME as a measure of school intake characteristics (2000) found it to be 'an inconsistent measure of poverty, and only a partial proxy for socio-economic circumstances.' Two decades later, the limitations she identified have, if anything, grown.
The most immediate problem is structural. Since January 2015, free school meals have been universal for P1–P3, and since January 2022, for P1–P5. This means that FME registration is no longer a meaningful deprivation proxy for the majority of the primary school population — the very population for which the ACEL data measures the attainment gap. The Scottish Government's own statistical publications acknowledge this directly.
For secondary pupils, FME remains means-tested and therefore theoretically usable as a deprivation proxy. But registration rates decline through the secondary years. This is not because fewer pupils are eligible — deprivation does not diminish as pupils age — but because registration requires an active claim, and many eligible families do not make one. The reasons are multiple: stigma, administrative barriers, lack of awareness, or simply the inertia of a process that requires parents to apply rather than being automatically enrolled. The result is that FME undercounts disadvantaged secondary pupils, and the undercounting is not random — it is more likely to affect families who are harder to reach, less engaged with school systems, and in some cases more disadvantaged than those who do register.
This matters practically because FME registration is the basis for Pupil Equity Funding (PEF) — the funding stream allocated directly to schools to address the attainment gap. PEF is calculated per registered FME pupil. A school whose eligible families do not register receives less funding than a school with the same level of deprivation whose families do. The measurement problem is therefore also a resource problem: the instrument that undercounts disadvantage also underfunds the response to it.
What this means for the gap
When the Scottish Government reports that the attainment gap has narrowed, it is reporting a comparison between SIMD Quintile 1 and Quintile 5 outcomes using data that is six years old and area-based, supplemented by FME data that structurally undercounts the disadvantaged population. This does not mean the reported narrowing is false. It may be genuine. But the margin of uncertainty around the measurement is larger than the confidence of the reporting suggests.
The measurement problems described here are not uniquely Scottish. England's reliance on FSM eligibility as a deprivation proxy faces the same registration gap — estimates suggest that a significant proportion of eligible families do not register, meaning the Pupil Premium cohort understates the true scale of disadvantage. The instruments are different; the breakage is the same.
Consider what a more accurate measurement might reveal. If SIMD data were current — reflecting the post-pandemic, post-cost-of-living-crisis geography of deprivation rather than the pre-pandemic geography — some data zones would shift quintile. Pupils currently classified as non-deprived would be reclassified. The denominator of the gap calculation would change. If FME registration were automatic rather than requiring an active claim — as it is in some English local authorities that use data-sharing between DWP and schools — the number of pupils identified as disadvantaged would increase, and the gap might widen rather than narrow, not because outcomes had changed but because the measurement had become more accurate.
The point is not that the attainment gap doesn't exist. It does, and the evidence for it is overwhelming. The point is that the instruments we use to measure it — and therefore to assess whether our efforts to close it are working — have known limitations that systematically undercount the disadvantaged population. If you are measuring with a ruler that is too short, you will underestimate the distance. And if you are congratulating yourself on the distance shrinking, you should first check the ruler.
What schools can do
This is not an argument that schools should wait for better national data before acting. It is an argument that schools should supplement the national measures with their own, more granular, more current understanding of who their disadvantaged pupils are and how they are doing.
Schools know things that SIMD does not. They know which families are struggling now, not six years ago. They know which pupils are not eating at home, which pupils are caring for siblings, which pupils have experienced a sudden change in circumstances that no area-based index will capture for years. This knowledge typically sits with pastoral staff — with guidance teachers, pupil support leaders, and the classroom teachers who see these young people every day. The challenge is connecting that knowledge to the attainment data, the attendance data, and the observation evidence that tells the school whether its interventions are reaching the pupils who need them most.
A school that relies solely on SIMD quintile and FME registration to identify its disadvantaged pupils is using the national instruments uncritically. A school that supplements these measures with its own pastoral intelligence — its own knowledge of which pupils are disadvantaged, regardless of what the national data says — is doing something more honest and more useful. It is measuring the gap as it exists in its own context, rather than as it is reported to exist by instruments that were designed for national comparison and are increasingly inadequate for school-level action.
The attainment gap is real. Closing it is urgent. But the first step in closing it is measuring it accurately — and the instruments Scotland currently uses are not as accurate as the confidence of the reporting implies.
The gap data matters most when it drives improvement priorities rather than just populating a dashboard.
Connecting gap analysis to what classrooms show is part of the same discipline — Learning Lens is available for Scottish schools — book a conversation from the home page if useful.
References
Croxford, L. (2000). 'Is Free-Meal Entitlement a Valid Measure of School Intake Characteristics?' Educational Research and Evaluation, 6(4), 317–335.
Scottish Government (2020). Scottish Index of Multiple Deprivation 2020. Edinburgh: Scottish Government.
Scottish Government (2025). Achievement of Curriculum for Excellence Levels 2024/25. Edinburgh: Scottish Government.
Scottish Government (2025). National Improvement Framework 2026: Improvement Plan. Edinburgh: Scottish Government.
Jamie Scobie writes from extensive experience in Scottish secondary education, including pastoral care, data for improvement, and school self-evaluation. This blog is an independent publication: he writes in a personal capacity as the creator of Learning Lens, writing about classroom observation, teaching evidence, and education policy. He speaks here only for himself and for Learning Lens, not for any employer or other organisation. He holds an MSt from Cambridge (Distinction) and a Masters from Stirling.