Using a randomized controlled trial, we examined the impact of a teacher professional learning (PL) program on English as a Second Language (ESL) teachers' use of evidence-based instructional strategies for multilingual learners, collaboration with classroom teachers, and incorporation of Latino multilingual learners' cultural wealth into their classrooms. Analyses included 29 ESL teachers from 29 elementary schools in three school districts. Teachers completed pre-post surveys and trained observers rated classroom instruction and cultural wealth for two cohorts of teachers in the yearlong program. Results showed that the PL program had a significant effect on ESL teachers' use of evidence-based instructional strategies. We also found a significant effect on ESL teachers' collaboration processes, including their use of an intentional framework for collaboration and their alignment with classroom teachers' instruction. We did not find differences between the PL group and the control group on ESL teachers' incorporation of cultural wealth in their classroom environment, or on the reported frequency of their collaboration.