This study estimates the causal effect of randomized offers of full-day versus half-day pre-K on students’ likelihood of having English language learner (ELL) 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 more than 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 a later ELL designation. Among students likely not fluent in English at pre-K entry, full-day pre-K offers reduce ELL designations in grades K–3 by 8–16 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 pre-K may be offset by reduced need for ELL services in the early grades—an important consideration for district leaders weighing the value of expanding program duration.
Malhotra et al. (Thu,) studied this question.