Tuesday, 6 November 2018

Converting 2018 KS2 scaled scores to standardised scores

Many schools are using standardised tests from the likes of NFER, GL and Rising Stars to monitor attainment and progress of pupils, and to predict outcomes; and yet there is lot of confusion about how standardised scores relate to scaled scores. The common assumption is that 100 on a standardised test (eg from NFER) is the same as 100 in a KS2 test, but it's not. Only 50% achieve 100 or more in a standardised test (100 represents the average, or the 50th percentile); yet 75% achieved 100+ in the KS2 reading test in 2018 (the average score in 2018 KS2 reading test was 105). If we want a standardised score that better represents expected standards then we need one that captures the top 75%, i.e. around 90. However, to be on the safe side, I recommend going for 94 (top 66%), or maybe even 95 (top 63%) if you want to be really robust. Whatever you do, please bear in mind that standardised test scores are not a prophecy of future results, they are simply an indicator. Michael Tidd (@ MichaelT1979) has written an excellent blog post on this subject, which I recommend you read if you are using standardised scores for tracking.

The purpose of this blog is to share a conversion table, that will give you a rough idea of how scaled scores convert to standardised scores. It is based on distribution of 2018 KS2 scores in reading and maths, taken from national tables. Download the national, local and regional tables (3rd link down) and click on table N2b. The cumulative percentages in table N2b are converted to standardised scores via this lookup table.

The scaled score to standardised score conversion table can be downloaded here.

Please note: this is not definitive; it is a guide. It will also change next year, when 2019 national data is released, but hopefully it will demonstrate that one score does not directly convert into another.


1 comment:

  1. This is extremely useful and something we have been talking about as part of our moderation of reading. Thanks! Great work as usual!