The randomized trial of the Making Socially Accepting Inclusive Classrooms (MOSAIC) program included intensive coaching from research staff to support teachers’ implementation of MOSAIC strategies and resulted in positive student outcomes (Mikami et al., J. Clin. Child Adolesc. Psychol. 51(6):1039–1052, 2022). However, these intensive procedures are costly (in time, money, and resources) and serve as barriers to intervention adoption under typical school conditions. In this study, we explored the extent to which MOSAIC-trained teachers could sustain practices under typical practice conditions (sustainment), the extent to which teachers who did not participate in the trial could adopt the practices under typical practice conditions (spread), and the extent to which strategy use in the follow-up year was associated with participation in MOSAIC-focused professional learning communities (PLCs). Participants were 30 elementary school teachers, including (a) 13 teachers who received intensive coaching on MOSAIC practices during the previous year (MOSAIC group), and (b) seven teachers who participated in the trial in the control condition, plus 10 new teachers interested in MOSAIC (new-to-MOSAIC group). We assessed MOSAIC strategy use over the school year via monthly observations and biweekly teacher self-report surveys. Observation data revealed high sustainment in the MOSAIC group, with teachers showing less than 20% decline in the use of most strategies between the two years of participation. New-to-MOSAIC teachers implemented some core MOSAIC strategies, although not to the extent as those in the MOSAIC group. Higher strategy use was modestly associated with PLC attendance. We discuss implications for encouraging sustainment and intervention spread after initial, intensive supports are withdrawn.