School boards have statutory authority over most elementary and secondary education policies, but receive little attention compared to other actors in education systems. A fundamental challenge to understanding the importance of boards is the absence of data on the policy goals of board members—i.e., their ideologies—forcing researchers to conduct tests based on demographic and professional characteristics—i.e., identities—with which ideology is presumed to correlate. This paper uses new data on the viewpoints and policy actions of school board members, coupled with a regression discontinuity design that generates quasi-random variation in board composition, to establish two results. The first is that the priorities of board members have large causal effects across many domains. For example, the effect of electing an equity-focused board member on test scores for low-income students is roughly equivalent to assigning every such student a teacher who is 0.3 to 0.4 SDs higher in the distribution of teacher value-added. The second is that observing policy priorities is crucial. Identity turns out to be a poor proxy for ideology, with limited governance effects that are fully explained by differences in policy priorities. Our findings challenge the belief that school boards are unimportant, showing that who serves on the board and what they prioritize can have far-reaching consequences for students.