Youth Mental Health First Aid (YMHFA) is a public education program designed to improve youth mental health outcomes by training adults to notice mental health problems and help youth in seeking treatment. This study used a pre-post 3-month follow-up design to explore whether mental health literacy (MHL), perceived mental health stigma (MHS), and confidence in helping behavior differed across time between Youth Mental Health First Aiders (i.e., involved in Project Advancing Wellness and Resilience in Education) who are and are not members of the mental health workforce. As expected at pretest, mental health workforce first aiders scored significantly higher than non-mental health workforce first aiders for MHL and confidence in helping behavior (p < 0.001), but no differences were found for MHS. Non-mental health workforce aiders scored significantly better from pretest to posttest for MHL and confidence in helping behavior (p < 0.001), to levels consistent with participants from the mental health workforce, who did not show improvements at posttest over relatively high pretest levels. With no additional training, non-mental health workforce participants were able to maintain the positive gains at the 3-month follow-up. Results suggest that YMHFA training is effective in increasing non-mental health workforce professionals' MHL and confidence to a level similar to that of their mental health workforce colleagues. Study findings suggest that YMHFA training may be too basic for mental health workforce professionals, and alternative trainings should be provided for them.