Evidence is just the start of finding what works

The example of education shows both the potential of evidence-based policy making, and the challenges facing it, argue Lee Elliot Major and Steve Higgins.

In England we spend around £2 billion a year on 170,000 teaching assistants in schools. The total impact of this money on the attainment of our children is zero. The best evidence we have indicates that for every TA who improves a pupil’s progress there is another whose deployment has a negative impact.

This is a powerful example of why we need evidence-based policy and practice, but it also highlights the difficulties of promoting changes to improve practice—because finding that TAs are deployed ineffectively does not tell you what to do about it.