“Whether educators have more time to enrich instruction or students have more time to learn how to play an instrument and write computer code, adding meaningful in-school hours is a critical investment that better prepares children to be successful in the 21st century,” Education Secretary Arne Duncan said in a statement.

The project comes as educators across the U.S. struggle to identify the best ways to strengthen a public education system that many fear has fallen behind other nations. Student testing, teacher evaluations, charter schools, and voucher programs join longer school days on the list of school reform initiatives that have been put forward with varying degrees of success.

The report from the center, which advocates for extending instruction time, cites research suggesting students who spend more hours learning perform better. One such study, from Harvard economist Roland Fryer, argues that of all the factors affecting educational outcomes, two are the best predictors of success: intensive tutoring and adding at least 300 hours to the standard school calendar.

More classroom time has long been a priority for Duncan, who warned a congressional committee in May 2009—just months after becoming education secretary—that American students were at a disadvantage compared to their peers in India and China. That same year, he suggested schools should be open six or seven days per week and should run 11 or 12 months out of the year.

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But not everyone agrees that shorter school days are to blame. A report last year from the National School Boards Association’s Center for Public Education disputed the notion that American schools have fallen behind in classroom time, pointing out that students in high-performing countries like South Korea, Finland, and Japan actually spend less time in school than most U.S. students.

The broader push to extend classroom time could also run up against concerns from teachers unions. Longer school days became a major sticking point in a seven-day teachers strike in September in Chicago. Mayor Rahm Emanuel eventually won an extension of the school day but paid the price in other concessions granted to teachers.

Just over 1,000 U.S. schools already operate on expanded schedules, an increase of 53 percent over 2009, according to a report being released Dec. 3 in connection with the announcement by the National Center on Time & Learning. The nonprofit group said more schools should follow suit but stressed that expanded learning time isn’t the right strategy for every school.

Some of the funds required to add 300 or more hours to the school calendar will come from shifting resources from existing federal programs, making use of the flexibility granted by waivers to No Child Left Behind. All five states taking part in the initiative have received waivers from the Education Department.