After determining the outcome and pre-test measure, comes the most important step in DIY evaluation: establishing a comparison group or ‘control’ in order to understand the impact of the approach you are testing.
Children will almost always progress as time passes, but you want to find out whether a new way of teaching means that they progress faster than usual. This means delivering the new approach to one group and then comparing to a group which is not receiving the new approach, or is instead receiving ‘business as usual’. The comparison between a group receiving the intervention and one continuing as normal, allows us to estimate what would have happened without the intervention, a concept known as “the counterfactual”. We can never truly know exactly what would have happened otherwise, but a control group proves the best possible estimate.
Before we look at different ways of establishing control groups, it is important to record some basic characteristics of your evaluation. The questions in the righthand box prompt you to think about the trial before it gets underway.