Lengthening the school day is a top priority for D.C. Chancellor Kaya Henderson, pictured here in July 2013. (Sarah L. Voisin/The Washington Post)

D.C. Chancellor Kaya Henderson has championed lengthening school days as one of her top priorities for improving schools and lifting student achievement, but her effort to expand the number of schools with longer days has been met with stiff resistance from the teachers union.

Eight D.C. traditional schools have experimented with longer days, and most have seen gains on standardized math and reading tests. Henderson set aside $5.1 million to add an hour of instruction at 42 more schools for the 2014-15 school year, but at almost all of those schools, teachers either voted against adopting the longer day or union members prevented the issue from coming up for a vote.

Only two schools — Amidon-Bowen Elementary in Southwest and Whittier Education Campus in Brightwood — voted to implement the longer day schoolwide in the fall.

An additional 16 did not have enough support to adopt the longer day schoolwide, but will move forward in part, using only those teachers who agree to work longer hours. Two dozen schools will not adopt a longer day in any form. Union officials had urged teachers not to agree to the change, arguing that it is a violation of their contract.

The Washington Teachers’ Union urged members to push back against a longer day, saying that the union contract calls for the issue to be taken up at the collective-bargaining table and not negotiated school by school.

Henderson, who has said that charter schools have demonstrated that extra instructional time can lift achievement among poor children, said she was disappointed that “the union took a stance that they wouldn’t allow the votes.”

“I think it’s shortsighted and I think that it robs young people, especially our struggling young people, of the opportunity to get more instructional time,” Henderson said. “I actually think when those teachers see huge gains and consequently get huge bonuses, I think the following year there might be more people who are apt to elect for extended day.”

Martin Welles, PTA president at Amidon-Bowen, said the extra hour each day will allow his school to partner with Navy Yard employees to offer a Lego robotics program, in addition to other instruction.

“Amidon-Bowen is a low-performing school on the rise. The extra hour of instruction, regardless of what is taught, is going to be beneficial to children,” he said. “This is the type of event that sends a signal . . . that Amidon-Bowen is one of these schools that’s trying hard to turn around and is going to do what it takes.”

Welles said it’s also a move that keeps the traditional school system competitive with the city’s fast-growing charter schools, many of which offer longer school days or an extended school year. “This is the type of thing DCPS needs to do in order to remain relevant,” he said.

Under the current teachers union contract, a school advisory committee composed of union members must consider and recommend any proposal for “nontraditional scheduling,” and then at least two-thirds of the school’s teachers must vote in favor of that proposal, before such scheduling can be implemented. And teachers must be paid an administrative premium — or about $34 per hour — for their additional time.

Union officials say that the nontraditional-scheduling provision allows for flexibility within the traditional 7.5-hour workday, not for longer workdays. Discussions about a longer workday must take place at the negotiating table as the two sides work on a new contract, union President Elizabeth Davis said.

“If you are asked to vote on an extended day, please VOTE ‘NO,’ ” Davis wrote in a message to union members in May. “To abstain from the vote could result in you being forced in extending your work hours without negotiation through your union. Vote No.”

Davis said in an interview last week that the union is “being cautious not to be roadblocks to reform, that is not even the issue. The issue is that we should both, DCPS and the WTU, respect the process.”

The union contract expired in September 2012, and by spring 2013 the school system and the union were close to reaching a deal that reportedly included longer school days. But negotiations had to start from scratch when then-union President Nathan Saunders lost his reelection bid to Davis in June 2013.

Negotiations have been stalled for months, with both sides blaming the other for delays.

Davis said that an extended day will be a top priority in the contract negotiations, but she isn’t sold on the idea that a longer day alone will produce achievement gains. Schools need a “better day” — with the resources that teachers and students need to succeed — before they need a longer day, she said.

School system officials said they anticipate using about $1.1 million of the $5.1 million budgeted for longer school days, but more schools could decide to adopt the longer days, at least partially, between now and August.

Most of the dozen principals The Washington Post contacted for this story did not return requests for comment about why their schools voted against implementing longer school days.

Mary Louise Jones, principal of McKinley Tech Middle School, said that a school advisory committee composed of union members did not allow a faculty-wide vote because of the union’s concerns. She said that when she polled teachers about implementing an extended-day program with certain grade levels or ability levels, teachers did not want to commit to a formal initiative even though they would have been paid extra, and even though many of them already volunteer to tutor after school.

“I also suspect that when we asked, it was the end of the year and teachers were experiencing school fatigue and this did not lend itself to asking them to consider doing even more,” Jones wrote in an e-mail. “Our teachers are great about providing extra help after school and I know that they will continue to do so next year.”