Don’t panic about quintiles

Ofsted have been placing schools into quintiles – bands comprising 20% of schools: bottom 20%, middle 20%, top 20% etc – in the IDSR for a few years now. Initially it was just based on progress scores but this year they have expanded the approach to include attainment at EYFS, KS1, KS2 and in phonics. With a reduction in the amount of data presented in the rest of the report, it is little surprise that schools are paying more attention to the quintile they have been placed in. And schools are starting to get twitchy, particularly when they find themselves in lowest bands. It’s therefore important that we have a better understanding of the data that underlies this broad approach to data presentation and realise that it’s not necessarily something to get concerned about.

The first thing to understand is that the big changes in results happen in the bottom (5th) and top (1st) quintile. In fact the really big changes happen in the first few percentiles at the top and bottom ends. After that it really levels out. This is illustrated in the following graph, which plots 2018 progress scores against percentile rank for all primary schools in England.

The graph shows that there is a very steep change in the results of schools in the top and bottom 5%. After that the gradient levels out and there is not a huge difference in progress scores between schools at the 20th and 80th percentile. In the above graph the progress scores of the middle 60% of schools ranges from -1.7 to +2.1. The quintile thresholds for 2018 reading progress scores are as follows:

  • Quintile 5: -21.6 to -1.8
  • Quintile 4: -1.7 to -0.4
  • Quintile 3: -0.3 to 0.7
  • Quintile 2: 0.8 to 2.1
  • Quintile 1: 2.2 to 11.6

Plotting results (in this case the % achieving expected standards in reading, writing and maths at KS2) produces a steeper gradient but we still have the greatest change in the bottom and top 10% of schools with less of a difference between schools ranked from the 20th and the 80th percentile, where results range from 52% to 79%.

The quintile thresholds for KS2 attainment in 2018 are as follows:

  • Quintile 5: 0-51%
  • Quintile 4: 52-62%
  • Quintile 3: 63-70%
  • Quintile 2: 71-79%
  • Quintile 1: 80-100%

Obviously there has to be a threshold somewhere and a change of 0.1 can move a school up or down a quintile. This is what happens when fine data is evaluated in such broad terms: it can make things look worse than they are; or it makes it look like there has been no change at all. As with all data, we need to see what lurks beneath.

Just don’t panic about quintiles.

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James Pembroke

Data Analyst and Advisor with 10 years experience in primary, secondary and post-16 sectors. Follow me on Twitter: @jpembroke

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