A meta-analysis is an analysis of a large number of studies and is used to try to draw out a general pattern from a very large number of results. Meta-analyses of educational research have become more popular in recent years, as a way of identifying methods and strategies that might have high probability of success in raising student attainment. However, a meta-analysis can only be as valid and reliable as the studies that it draws upon – so the recommendations that arise from these studies come with significant caveats.
To compare different teaching strategies, a meta-analysis will use ‘effect sizes’. An effect size of 1.0 indicates that a strategy has advanced the learning of students in the study by one standard deviation above the mean. An effect size of 1.0 is often presented as equivalent to about 2 GCSE grades – so a very large positive effect.
Here is an example from John Hattie, who conducted a meta-analysis of over 52,000 studies:
Professor John Hattie’s meta-analysis
A more detailed look at these strategies and the effect sizes associated with them can be found from John Hattie’s own website.
Evidence into Practice 
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