In response to concerns about the efficacy of the U.S. education system, a number of school reforms have been attempted. This article briefly presents an argument explaining why the current public school system will not efficiently produce educational services and the role of charter schools in improving public school efficiency. It then examines empirically, for a set of charter schools managed by National Heritage Academies (NHA), the effect of time spent at school as a measure of value added in the educational process. The finding is that for NHA schools, time spent has a statistically significant positive effect on test scores. (Contains 13 tables and 29 notes.)