Our field of couple and family therapy focuses on change, different ways people change, and how therapists can facilitate change. Change can be modeled as an average trajectory—growth curve model—or as multiple classes of trajectories—growth mixture model. The field of MFT has not yet fully embraced implementing more advanced longitudinal modeling procedures to study what we care about most, change across time. To support our field moving in this direction, we provide a step-by-step description and example in Mplus software. Our example analysis used N = 5,958 participants from the Add Health dataset, to identify unique classifications of trajectories of binge drinking. We discuss how these analytical methods provide increased options to advance family science and clinical research.