The NFER Education Trials Unit

An introduction to randomised controlled trials

A randomised controlled trial (RCT) seeks to measure impact by identifying a causal link between an intervention and change. A RCT is a trial carried out on two (or more) groups where participants are randomly assigned to either an ‘intervention’ (i.e. the intervention group) or ‘controlled condition’ (i.e. the control group). Each group is tested at the end of a trial and the results from the groups are compared to see if the intervention has made a difference, in other words, has the intervention achieved its desired outcome? If the randomised groups are large enough, we can be confident that differences observed are due to the intervention and not some other factor.

RCTs are highly regarded by many organisations involved in education research including the Department for Education (DfE) and the Education Endowment Foundation (EEF). As with any research methodology, RCTs have their place and are not suitable for all research and evaluation.

A RCT is usually run alongside a process evaluation of a programme or intervention to see how the intervention has been implemented. This often takes the form of qualitative interviews and seeks to find out if the intervention has been carried out as intended. This checks the fidelity of the intervention and is crucial before assumptions are made about what the results mean. For example, if one teacher is following the intervention in every lesson but another teacher only does the intervention in one lesson a month, this will mean that the groups are not comparable.

Find out more with our two guides: