LOS ANGELES — Five states will experiment with giving pupils additional instruction and other support by 300 hours a year of teaching time to the school year, officials announced Monday.

The program, starting next year in some schools in Colorado, Connecticut, Massachusetts, New York and Tennessee, is designed to increase student achievement and make U.S. education more competitive globally, a goal of the Obama administration.

The three-year pilot program will affect almost 20,000 students in 40 schools in the next three years, with the hope of expanding the effort to include more schools down the road. Educators and parents will decide whether to lengthen the school day or add days to the school calendar, or both.

“I’m convinced the kind of results we’ll see over the next couple of years, I think, will compel the country to act in a very different way,” Education Secretary Arne Duncan said Monday.

Most schools have varying hours, but in general, classes in most states run from around 8 a.m. to 3 p.m., depending on grade. After-school programs often depend on local funding.

The program is getting federal, state and local funding as well as backing from private groups, such as the Ford Foundation and the National Center on Time & Learning, a nonprofit research and advocacy group.

The effort comes after more than 1,000 schools, including many charter schools, have added hours, arguing that keeping students on campus for more hours leads to improvement, even if the additional time goes to extracurricular activities.

Adding school time to primary subjects, such as math and reading, can lead to higher scores, supporters say, and adding extracurricular subjects, such as music or art, can give children exposure to subjects they may not normally get.

“That extra time with their teachers or within a structured setting means all the world,” said Colorado Gov. John Hickenlooper. “It means it allows them to continue the momentum they had the day before. It means they don’t slip back over the summer. It allows them to really deliver.”

The Obama administration has advocated more classroom time. In 2009, Duncan told lawmakers that U.S. students were at a disadvantage compared with India and China. That same year, he suggested schools should be open six or seven days a week and should run 11 or 12 months out of the year. But not everyone agrees that simply adding instructional time benefits students.

The National School Boards Association’s Center for Public Education last year questioned whether U.S. students spend less time in classrooms than those overseas. Pupils in countries where students perform well on tests — such as South Korea, Finland and Japan — actually spend less time in school than most U.S. students, the group said.