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 misconception 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 79% achieved 100+ in the KS2 reading test in 2019 (the average score in 2019 KS2 maths test was 105). If we want a standardised score that better represents expected standards then we therefore need one that captures the top 79%, i.e. a standardised score of around 88. However, this is rather low top adopt as a threshold and, to be on the safe side, I recommend opting for 94 (top 66%) or 95 (top 63%) if you want to be more robust. Whatever you do, please bear in mind that standardised test scores are not a prophecy of future results, they are simply an indicator, and may not correlate strongly with KS2 scores.
I have written a blog on the pros and cons of standardised tests here, and Michael Tidd (@ MichaelT1979) has also written an excellent blog post on the 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, which will give you a rough idea of how scaled scores convert to standardised scores. It is based on distribution of 2019 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 2020 national data is released, but hopefully it will demonstrate that one score does not directly convert into another.