The effects of a positive mindset trigger word intervention on the expressive performance of individual junior high singers were tested in this study. Participants (N = 155) were assigned randomly to a control group or an experimental group. Members of the experimental group participated in a 40-min intervention while members of the control group participated in normal rehearsal. The intervention involved a pre-performance routine of breathing and silently repeating the words "bold", "confident", and "free". It also involved practice activities for applying the technique to performance. Participants were tested individually directly before and after the intervention and 2 weeks later. Results indicated a significant positive effect on Overall Expressive Performance (p less than 0.001) and on the subcategories Dynamics (p less than 0.001), Performance Factors (p less than 0.001), and Timing (p less than 0.001). There was no significant effect on subcategories Articulation (p = 0.195) and Tone (p = 0.035). Implications were that (1) use of positive mindset trigger words in a pre-performance routine may bring immediate improvement in expressive performance for junior high age singers, (2) junior high age singers may possess higher levels of expressive performance skill than they or teachers recognize, and (3) review and repetition likely are needed for junior high age students to retain the intervention benefits. (Contains 4 tables and 1 figure.)