Additional months' progress

The impact measure shows the number of additional months of progress made, on average, by children and young people who received the intervention, compared to similar children and young people who did not.

For example, the 'Feedback' strand shows that in the research studies included in the Toolkit, improving the quality of feedback had an average impact of 8 additional months’ progress.

This means that pupils in the classes where feedback interventions were provided made, on average, 8 months' more progress than similar pupils in other classes.

The months of additional progress estimates are based on ‘effect sizes’ reported in British and international research studies.

Effect sizes describe the size of the difference between two groups in a standard and comparable way. However, it can be difficult to understand what a given effect size actually means for the progress of children and young people. That is why the the EEF translates effect sizes into the months’ progress measure, as shown in the table below.

Months' ProgressEffect size
-0.010.01Very low or no impact
10.020.09Low impact
20.100.18Low impact
30.190.26Moderate impact
40.270.35Moderate impact
50.360.44Moderate impact
60.450.52High impact
70.530.61High impact
80.620.69High impact
90.700.78Very high impact
100.790.87Very high impact
110.880.95Very high impact
120.961.00Very high impact

Notes: (i) Effect sizes are presented to the nearest 2 decimal places. (ii) For negative effect sizes, the conversion from effect size to months of additional progress is of the same size as shown in the table but negative in value. If the months' progress figure is negative, this does not necessarily imply negative progress. It means that individuals have made less progress than would be expected without the intervention. (iii) The conversion from effect size to additional months' progress differs slightly between the Toolkits and the reports of individual EEF-funded projects. For more information on the conversion for individual projects see here

The Toolkits prioritise effect sizes derived from systematic reviews of research and meta-analyses of studies. Approaches are only included in the Toolkits if there are effect sizes available which can be used to create a months’ progress estimate. 

For more detail on how the months progress measure is developed see the Toolkit Manual