We investigate the role of teachers' unions in state policymaking in the context of "No Child Left Behind." Our analyses of panel data show that political party control and region moderate the influence of teachers' unions in the adoption of accountability policies by states. Our analyses of marginal effects show that teachers' unions are not always against the adoption of stronger accountability policies and neither do they always align with the Democratic Party. Our findings suggest that the current dominant prescription in the policy debate for curtailing the collective bargaining rights of teachers' unions is not fully substantiated.