At a time when policymakers are demanding budget cuts and more innovative approaches to schooling, pressure is building for loosening up constraints on class sizes. After dropping for decades, average class sizes in American schools may be growing again as schools cope with budget shortfalls. Although some educators see the rising numbers as a worrisome trend, others see an opportunity for innovation. The national ratio of students to their teachers fell between 1980 and 2008, from 17.6 to 15.8 students per public school teacher, according to the National Center for Education Statistics. Because the statistics count special education and other specialized teachers who normally have much smaller classes than regular teachers do, the U.S. Department of Education estimates the current average class size at more like 25 students. That number is likely to rise, given states' and districts' financial constraints, Secretary of Education Arne Duncan said last month at a Washington forum. Nearly all the states that have changed their class-size laws since 2008 have relaxed restrictions, in many cases specifically to ease districts' budget burdens, according to the Denver-based Education Commission of the States. Yet what constitutes "evidence-based" reduction has been at the crux of the class-size debate for more than a quarter-century. Proponents of reducing class size argue that it is the simplest, most direct way to improve student achievement, while skeptics argue that the small, generalized reductions that result from most state policies don't provide enough improvement to justify their cost.