Data on implementation of school-based interventions adds highly valuable information to corresponding evaluation studies. Measuring implementation outcomes, such as fidelity or acceptability, provides information on how to improve current and future implementation processes. Moreover, analyzing intervention outcomes in combination with implementation outcomes sheds light onto the reasons for variabilities in an intervention's effectiveness in different schools. The present paper provides a brief introduction to evaluating the implementation of school-based interventions. First, different types of implementation outcomes and approaches for selecting appropriate outcomes are introduced. Subsequently, measurement issues associated with implementation evaluation in school settings are discussed. Finally, requirements and advantages associated with linking implementation outcomes to intervention outcomes in data analyses are presented. The information is expected to be useful for researchers who are evaluating school-based interventions and especially for those who are new to the field of implementation evaluation.