The Systemic Clinical Outcome and Routine Evaluation version 15 (SCORE-15) is a measure used to assess family-level change in family therapy. The SCORE-15 has been demonstrated to be a reliable and valid measure, with high clinical utility; however, the SCORE-15 lacks the ability to determine whether the change in family functioning during the course of therapy is clinically significant. This study aimed to establish a reliable change index (RCI) and clinical cutoff score so that researchers and clinicians can determine clinically significant change in family therapy. US samples of 71 clinical participants and 244 community participants completed the SCORE-15. Results indicated a cutoff score of 40.37 and an RCI of 9.52. Consequently, family members who improve their SCORE-15 score during the course of therapy by at least 9 points and who cross the threshold of 40 during the course of therapy are considered to have experienced clinically significant change.