The randomised controlled trial (RCT) is an evaluative method used by social scientists in order to establish whether or not an intervention is effective. This contribution discusses the fundamental aspects of good RCT design. These are illustrated through the use of a recently completed RCT which evaluated an information and communication technology (ICT) intervention designed to improve the literacy (reading and spelling) abilities of 11- and 12-year-old children. Some of the limitations of this trial are discussed and suggestions outlined for how it could have been improved. It is demonstrated that it is possible to evaluate a widely-used intervention in a rigorous fashion and to obtain educationally meaningful results, which are of interest to the practitioner, policy maker and researcher.