Although preventing youth overweight and obesity is a public health priority, quality physical education (PE) is marginalized in practice. In May 2014, we estimated energy expenditure (EE; derived from PE frequency, duration, and intensity; mean student mass; and class size) from national recommendations and data from the 19 US states with PE duration guidelines, under 3 scenarios: potential (quality PE, defined as 50% moderate-to-vigorous physical activity [MVPA]), reality (MVPA = 35%), and classroom instruction only. Students in schools following nationally recommended PE standards from grades 1 through 10 could expend from 35 000 to 90 000 more kilocalories than students who received classroom instruction instead. PE's potential for increasing student EE will only be realized with stronger school policies and increased accountability.