Charter schools are the most popular form of school choice in the US. However, we know little about how these schools affect traditional public schools. I look at how charter schools affect achievement, behavior, and attendance in nearby traditional public schools using data from a large urban school district in the southwest. Unlike prior work that relies on school fixed effects, I instead address the endogenous location of charter schools using an instrumental variables strategy. My results show that when charter school penetration increases, students suffer modest but statistically significant drops in math and language score gains. However, achievement losses are potentially offset by improvement in discipline.