Despite the 1982 Supreme Court decision "Plyler v. Doe," little guidance has been provided on how to support undocumented students. Although education scholars have explored undocumented students' experiences, little research examines the effects of professional development on pre-service school professionals' understanding regarding policies and factors impacting undocumented students and their families. Since school professionals can be allies, and schools can provide safe spaces, this quantitative study investigated the effectiveness of two professional development opportunities- a two-hour, in-person training, and a film training- for pre-service school professionals focused on increasing their understanding of policies and factors impacting undocumented students. Findings indicated greater effectiveness for the in-person training when compared to the film training, and also indicated minimal differences in pre-post scores when comparing participants by race/ethnicity and level of experience on the topic. The results suggest that effective professional development can improve school professionals' understanding of advocacy and support.