In many intervention and evaluation studies, outcome variables are assessed using a multimethod approach comparing multiple groups over time. In this article, we show how evaluation data obtained from a complex multitrait-multimethod-multioccasion-multigroup design can be analyzed with structural equation models. In particular, we show how the structural equation modeling approach can be used to (a) handle ordinal items as indicators, (b) test measurement invariance, and (c) test the means of the latent variables to examine treatment effects. We present an application to data from an evaluation study of an early childhood prevention program. A total of 659 children in intervention and control groups were rated by their parents and teachers on prosocial behavior and relational aggression before and after the program implementation. No mean change in relational aggression was found in either group, whereas an increase in prosocial behavior was found in both groups. Advantages and limitations of the proposed approach are highlighted.The use of multiple methods to ensure the valid measurement of a construct found its way into common practice after Campbell and Fiske's (1959) seminal paper introduced the multitraitmultimethod (MTMM) approach. In MTMM studies, several constructs are assessed by two or more methods (e.g., ratings of depression and anxiety by therapist and patient or by mother and child). Multimethod data not only provide information about convergent and discriminant Correspondence should be addressed to Claudia Crayen,