I don’t know about this. Ask me again in the summer. Right now it seems like every school day lasts about 19 hours!

School hours in the United States were developed during the 19th century, in part to allow students to help their families with farm work in the afternoon. We are no longer an agrarian economy, but most schools still get out around 3 p.m.

It’s time for a change: Schools should remain open until 5 or 6 p.m. The result would be better-educated students and less-stressed parents.

A longer school day, especially if combined with other steps such as intensive tutoring and frequent feedback to teachers from administrators, could improve academic achievement. For example, Roland Fryer and Will Dobbie of Harvard University have found that a longer day is a key aspect of high-performing charter schools in New York. Fryer found similar results for traditional middle and high schools in Houston: Implementing reforms there, including a longer school day, produced large gains in math performance (albeit modest to no gains in reading). More time at task improves student achievement.

A longer school day also would reduce the number of latchkey kids. The Afterschool Alliance has found that 15 million children, sometimes as young as 5, are left unsupervised after school. Not surprisingly, unsupervised children tend to get into trouble.

Teachers and assistants would need to be paid more — and perhaps more would need to be hired. In 2008, the Center for American Progress estimated that expanding learning time by 30 percent — or adding between 90 minutes and two hours to the school day — would add 6 to 20 percent to school budgets. To improve student achievement and worry less about latchkey children, that’s a price worth paying.