DES MOINES, Iowa (AP) — The Iowa Department of Education says school districts seeking permission to start classes earlier in the summer must prove that academic achievement is at risk. The Des Moines Register reported Wednesday the department sent the new guidelines to school districts. The guidelines say districts must show students would be affected in a “negative and significant manner” if classes start during the week of Sept. 1. Districts must provide research backing up the claim.

Last month, department Director Brad Buck told districts the state would stop granting automatic waivers to school districts seeking to start classes earlier in the summer. State law requires districts to start school no earlier than the calendar week including Sept. 1 but in the past, most have obtained waivers allowing them to begin classes earlier.