A new report from researchers at the University of Montana shows shorter school weeks may hurt student performance and school budgets, according to a report from Montana Public Radio.

While a growing number of schools in Montana have switched to four-day weeks, the researchers say data analysis on four-day school weeks “demonstrates a disturbing trend for education in Montana.” They found that student performance under four-day school weeks declines the longer a district uses the schedule, and lags behind kids in traditional five-day weeks.

Schools with shorter weeks often spend more on instruction, maintenance, transportation and food per student than similarly sized schools on a five-day schedule. A typical Class-B school in Montana would likely spend about $100,000 more annually after transitioning to a four-day week, according to the report.

State lawmakers allowed schools to switch to four-day instruction in 2005. Since then, 260 mostly small schools have adopted the schedule. District leaders have suggested shorter weeks could help them recruit and retain teachers. But the researchers say more evidence is needed to prove or disprove that argument.

The report’s authors recommend a return to five-day school weeks statewide.