The Effect of Full- vs. Half-Day Pre-K on Grade K-3 English Learner Designations

This study estimates the causal effect of randomized offers of full-day versus half-day pre-kindergarten on students’ likelihood of having English learners (EL) designations in early elementary grades. We leverage a randomized controlled trial in a Colorado district serving primarily low-income, Latinx families, where students assigned to full-day pre-K received over twice as much instructional time. Although instruction was not formally multilingual, we hypothesize that additional English exposure in full-day classrooms may reduce the likelihood of later EL designation. Among students likely not fluent in English at pre-K entry, full-day offers reduce EL designations in grades K-3 by 8 to 16 percentage points. These findings contribute to evidence on the long-term benefits of full-day pre-K and suggest the added costs of full- versus half-day may be offset by reduced need for EL services in the early grades—an important consideration for district leaders weighing the value of expanding program duration.