This report is designed to provide practical guidance on how to address the problem of missing data in the analysis of data in Randomized Controlled Trials (RCTs) of educational interventions, with a particular focus on the common educational situation in which groups of students such as entire classrooms or schools are randomized (called Group Randomized Trials, GRTs). The need for such guidance is of growing importance as the number of educational RCTs has increased in recent years. For example, the ten Regional Educational Laboratories (RELs) sponsored by the Institute of Education Sciences (IES) of the U.S. Department of Education are currently conducting 25 RCTs to measure the effectiveness of different educational interventions, and IES has sponsored 23 impact evaluations that randomized students, schools, or teachers since it was established in 2002.