Background: Establishing what constitutes clinically significant change is important both for reviewing the function of services and for reflecting on individual clinical practice. A range of methods for assessing change exist, but it remains unclear which are best to use and under which circumstances. Method: This paper reviews four indices of change [difference scores (DS), crossing clinical threshold (CCT), reliable change index (RCI) and added value scores (AVS)] drawing on outcome data for 9764 young people from child and adolescent mental health services across England. Results: Looking at DS, the t-test for time one to time two scores indicated a significant difference between baseline and follow up scores, with a standardised effect size of d = 0.40. AVS analysis resulted in a smaller effect size of 0.12. Analysis of those crossing the clinical threshold showed 21.2% of cases were classified as recovered, while 5.5% were classified as deteriorated. RCI identified 16.5% of cases as showing reliable improvement and 2.3% of cases as showing reliable deterioration. Across RCI and CCT 80.5% of the pairings were exact (i.e., identified in the same category using each method). Conclusions: Findings indicate that the level of agreement across approaches is at least moderate; however, the estimated extent of change varied to some extent based on the index used. Each index may be appropriate for different contexts: CCT and RCI may be best suited to use for individual case review; whereas DS and AVS may be more appropriate for case-mix adjusted national reporting.