There is ongoing debate in the United States about just how diverse, inclusive, and equitable the opt-out movement--and grassroots education activism more broadly--has been over the past decade. Today, a prevailing stereotype holds that the opt-out movement predominantly mobilizes white, middle-class, and suburban parents and is therefore a force for educational privilege, not equity. However, this stereotype has never been rigorously tested and it is still an open question as to how opt-out movement participants differ from non-participants, especially along the lines of race and class. Leveraging a comprehensive quantitative dataset of New York school district opt-out rates and community characteristics as well as original case study data collected from four purposefully sampled New York school districts, this study uncovers evidence challenging the dominant narrative of opt-out participation. It finds that the opt-out movement has been active across a diversity of district contexts and, with only small qualifications, has simultaneously mobilized a diverse cross section of parents within districts. However, the most active and longest-tenured opt-out parents do appear to be whiter and wealthier than the movement as a whole. This paper concludes by discussing the implications of these findings for our understanding of the U.S. opt-out movement as well as the potential of grassroots educational activism to be a force for equity and inclusion in U.S. education politics more generally.