More "structured learning." Longer school days. Block scheduling. Year-round schools. The list of well-intentioned school reforms and reform proposals targeting the use of time goes on and on. Four years ago this April, the U.S. Department of Education published Prisoners of Time, a report that called for radical rethinking of the time/schooling formula. Striking a somewhat alarmist tone, its authors warned that "American students must have more time for learning. The six-hour, 180-day school year should be relegated to museums, an exhibit from our education past." U.S. students spend far less time on core subjects than students in France, Germany, and Japan, argued the authors, warning that the use of time in U.S. schools is "a recipe for a kind of slow-motion social suicide."

But does giving students more time to learn necessarily mean that they will learn more? Does changing the school day or year change learning in any meaningful way? Research and experience point to a complex set of answers affected by a host of other variables.