Studies of the charter sector typically compare charters and traditional public schools at a point in time. These comparisons are potentially misleading because many charter-related reforms require time to generate results. We study quality dynamics among Texas charter schools from 2001-2011. School quality in the charter sector was initially highly variable and on average lower than traditional public schools. However, exits, improvement of existing charter schools, and expansion of higher-performing charter management organizations increased charter effectiveness relative to traditional public schools.  We present evidence that reduced student mobility and an increased share of charters adhering to No Excuses- style curricula contribute to these improvements.