Financial incentives for teachers to increase student performance is an increasingly popular education policy around the world. This paper describes a school-based randomized trial in over two-hundred New York City public schools designed to better understand the impact of teacher incentives on student achievement. I find no evidence that teacher incentives increase student performance, attendance, or graduation, nor do I find any evidence that the incentives change student or teacher behavior. If anything, teacher incentives may decrease student achievement, especially in larger schools. The paper concludes with a speculative discussion of theories that may explain these stark results.