Public-school policy and federal law both emphasize parental involvement, yet there is insufficient research guiding meaningful collaboration between school practitioners and immigrant parents. This article reports on results gleaned from a larger study of school-based adult ESL classes, focusing on the role that these classes could play in supporting effective parental involvement. The focal study was quasi-experimental and included Mexican mothers previously enrolled in school-based ESL classes (N = 87). Analysis included mixed-methods data drawn from treatment and control groups (N = 8). This article presents the results of an intervention that guided treatment-group ESL teachers to integrate parent-involvement knowledge and behaviors into instruction, in comparison to a form of ESL classes typically offered in public schools. The final analysis reveals a significant increase in both ESL and parent-involvement skills acquired by the students in the treatment group. It also demonstrates numerous ways that the intervention supported meaningful parent-school collaboration, reflecting new knowledge and behaviors, on the part of both the Mexican mothers and school staff. Thus the study yields implications for practice as well as theory development in the field of parental involvement. (Contains 7 endnotes and 2 tables.)