Because they provide data on responsiveness to experimental manipulation, clinical trials involving mindfulness-based interventions are a source of evidence for the construct validity of self-report measures of mindfulness. Within-group and between-group changes in mindfulness were examined from randomized clinical trials comparing mindfulness interventions to other bona fide treatment comparison conditions or waitlist control conditions. We also examined changes in clinical outcomes and the magnitude of these changes relative to changes in mindfulness. We included 69 published studies representing 55 unique samples (n = 4743). Self-report mindfulness measures showed relatively larger gains in mindfulness intervention conditions vis-à-vis waitlist comparison conditions at both post-treatment (effect size [ES] = 0.52, 95% CI [0.40, 0.64]) and follow-up (ES = 0.52 [0.20, 0.84]), although the effect at follow-up diminished to non-significance in a trim-and-fill analysis intended to account for publication bias (ES = 0.35 [− 0.03, 0.72]). Measures of mindfulness also showed relatively larger gains in mindfulness intervention conditions vis-à-vis bona fide comparison conditions, but only at post-treatment (ES = 0.25 [0.11, 0.38], 0.10 [− 0.08, 0.28], at post-treatment and follow-up, respectively). All three conditions (mindfulness, bona fide, waitlist) showed relatively larger improvements on measures of clinical outcomes than measures of mindfulness, with the exception of waitlist conditions for which this effect was no longer significant at follow-up. Taken together, findings provide partial support for the unique responsiveness of mindfulness self-report measures to interventions that include promotion of mindfulness meditation practice.