In 2020, the ECLS-K:2024 tested the design, procedures, and instruments for possible inclusion of a national spring preschool round. A sample of schools educating students of kindergarten age were selected. Within sampled school catchment areas, address-based sampling (ABS) was used to select a sample of residential addresses to screen for the presence of young children in the household. Approximately 28,000 households were screened in spring 2020 to identify children who planned to attend kindergarten (or a kindergarten equivalent) in fall 2020. Mailings directed respondents to web screeners and, for those households with children of preschool age, parent surveys. Screeners and parent surveys were also available in paper format for households that did not complete them online. Approximately 300 parents completed the full spring parent survey. In fall 2020, a follow-up data collection was conducted with those parents to determine whether the children matriculated into kindergarten as planned and, if so, which schools they attended.

In the fall of 2022, a small, trial run of the ECLS-K:2024 was conducted to make sure the study activities worked as and to test the national study's kindergarten and first-grade instruments. Fifty schools were sampled from five geographic sites and asked to participate in the K-1 FT. Within each geographic area, the samples represented different urbanicity levels and included public and private schools. In each of the schools, eligible kindergarten, first-grade, and second-grade students and their school administrators, teachers, and parents were selected to participate. The student data were used to develop assessments for the kindergarten and first-grade national ECLS-K:2024 data collections. The school administrators, teachers, and parents provided information needed to finalize the national study's survey instruments.