Coach development programs should target coaches' interpersonal behaviours (Lefebvre et al., 2016), be informed by behaviour change techniques (Allan et al., 2017), and be subjected to comprehensive evaluations (Evans et al., 2015). As such, informed by the full-range leadership model (Bass & Riggio, 2006) and the Behaviour Change Wheel (Michie et al., 2011), Turnnidge and Côté (2017a) developed the Transformational Coaching Workshop (TCW), which offers training on a range of interpersonal behaviours. The purpose of this study was to evaluate the TCW's impact by observing coaches' behaviours. Participants included 8 male head coaches of youth competitive soccer teams. Systematic observation using the Coach Leadership Assessment System (Turnnidge & Côté, 2016b) was employed pre- and post-workshop to examine coaches' leadership behaviours. Paired samples t-tests, bootstrapped confidence intervals, and effect sizes indicated that idealized influence (p = .067, d = .76, [-114.03, -7.64]), inspirational motivation (p = .087, d = .70, [-265.42, -2.92]), and intellectual stimulation (p = .132, d = .60, [-171.51, -1.25]) behaviours had confidence intervals that did not cross zero and medium to large effect sizes – suggesting that coaches engaged more in these three transformational leadership (TFL) behaviors after the workshop. Furthermore, coaches spent significantly less time displaying neutral (p = .007, d = 1.34) and organizational (p = .001, d = 1.90) behaviours, yet significantly more time displaying leadership through instruction/feedback (p = 0.013, d = 1.17) after the workshop. Overall, this study offers support for providing TFL-theory informed education to youth sport coaches.