At first blush it seems almost silly to have a symposium on the impact of added time in instruction on student outcomes. After all, a higher dosage of teaching should obviously produce more learning. In reality, the prior research on this question has been quite inconclusive. This symposium, however, moves knowledge forward a considerable distance. The two papers – by Victor Lavy and by Steven Rivkin and Jeffrey Schiman – advance our understanding in three different areas. First, the substantive conclusions about the positive impact of added time help to remove uncertainty about effects and provide direct policy guidance. Second, each of the papers addresses the methodological issues that have plagued prior research in a careful and thoughtful way. These ideas on approach go beyond just the evaluation of time use in the classroom. Third, by providing intriguing insights into variations of effects across countries, both underscore the value of comparative international studies.