After millions of American schoolchildren fell behind during the COVID-19 pandemic, some states and school districts are looking at year-round school calendars as a way to recoup lost learning. Typically, year-round calendars don't increase learning time but rather spread school days more equally across 12 months, with a shorter summer vacation and longer breaks throughout the year. Year-round calendars are often presented as a novel approach to accelerate student learning. But they have been tried and tested for over 50 years, and rigorous research on nearly one thousand public schools in the United States has found that they don't raise academic achievement. Meanwhile, they needlessly complicate life for working parents and teachers.