In this file photo from 2010, Arlington students visit a planetarium. (Evy Mages/For The Washington Post)

Even institutions as successful as the Chicago Cubs, Apple and the U.S. Army make mistakes, so I’m not surprised that principals in one of the most effective school districts in the country, Arlington County, are making a dubious policy move and not explaining it well to parents.

Arlington’s middle school principals are exploring changes that include a switch to block scheduling. That would mean replacing the traditional daily class periods with classes that meet every other day and could be twice as long.

Many people, including me, think block scheduling is an attractive but unproductive fad. A 2006 University of Virginia study said students in high school block schedules did somewhat worse in college sciences than those who had regular schedules. A 2010 review of British research said block schedule results were slightly positive but “are not strong enough to recommend their implementation.”

What Arlington does could affect what has been a sweeping trend in the Washington area. The every-other-day class system was hot in the 1990s. Since then, some schools have switched back to traditional scheduling, but the issue is rarely discussed. Parents in Arlington say they are having trouble getting answers to their questions, a consistent failing of all school districts, good and bad.

Arlington Schools Superintendent Patrick Murphy proposed block schedules for all middle schools in 2012. He said regular periods were too short for the kind of creative teaching early adolescents need.

“We are doing a disservice to students to run them through a seven-period day with a 45-minute turnaround,” he said.

This time, however, he is not pushing the change. Arlington schools spokeswoman Linda Erdos said principals are taking the initiative. Murphy is allowing them “to explore options with their communities,” she said.

Only one Arlington middle school, Kenmore, has gone to a block schedule, and just for sixth-graders. “This type of schedule carries quite a few risks,” said Williamsburg Middle School parent Lauren LeMay. “We would like to know exactly what they’re trying to accomplish at Williamsburg and why they think block scheduling is the answer.”

Parents say they worry about damage to music and language instruction and a lack of supporting research.

Those concerns seem basic compared with the complex characterization of the schedule changes offered by Tara Nattrass, assistant superintendent for instruction. The middle schools are looking for “more personalized learning opportunities for students,” she said. They have “been exploring strategies for this approach including personalizing teacher advisory time, revisiting master schedules and providing blocks of time for small group instruction.”

That’s pretty vague. I see why the parents are frustrated. They have not gotten a clear answer to one of their greatest concerns: What happens to classes that need much repetition, such as band and orchestra?

“One of the most negative and lasting impacts of full block scheduling is the elimination of cross-grade groupings,” said Swanson Middle School band parent Cathy Celestino. That means schools might not be able to assign students of similar skill level from different grades to the same band class.

It could also make it difficult to arrange daily practice. A group of parents and community members called Arlington Parents for Effective Scheduling concluded that the research shows that “daily instruction is a critical component of effective teaching and learning in math and foreign language,” Celestino said.

Parents say Williamsburg Principal Gordon Laurie is privately presenting the switch to block scheduling as a given and is asking teachers what kind of block schedule would be best. Williamsburg parent Patty Donmoyer said that a meeting Laurie had with parents Nov. 9 did not shed much light. “They never asked us if block scheduling should happen,” Donmoyer said. “Now we’re being given only minimal input on how it will happen.”

Arlington’s long record of success suggests it might make this work even without much research. But all districts need to give parents and teachers more chances for discussion and understanding before making such moves.