Three-level models for indirect effects in school- and class-randomized experiments in education

Due to the clustered nature of field data, multi-level modeling has become commonly used to analyze data arising from educational field experiments. While recent methodological literature has focused on multi-level mediation analysis, relatively little attention has been devoted to mediation analysis when three levels (e.g., student, class, school) are present in a study setting. This article presents analysis models that can be used to test indirect effects in experimental designs having three levels where random assignment is at the third (school) or second (class) level and where the indirect effect may be random. In the presentation, simulated datasets are used to illustrate model specification and results interpretation for hypothetical three-level educational experiments involving mediation and moderation of treatment effects.