Onwuegbuzie and colleagues proposed the Instrument Development and Construct Validation (IDCV) process as a mixed methods framework for creating and validating measures. Examples applying IDCV are lacking. We provide an illustrative case integrating the Rasch model and cognitive interviews applied to the development of the Transformative Experience Questionnaire (TEQ). TEQ measures student engagement with the content they are learning. IDCV process yielded a high degree of utility for informing the psychometric properties of the TEQ. The quantitative data yielded supportive content, construct, and concurrent-related validity evidence using a sample of middle (n = 115) and high school students (n = 81). The qualitative data revealed item rewording was needed. Moderate to strong test–retest reliability was found for both forms.