The Madison Metropolitan School District (MMSD) began offering free, universal, half-day four-year-old kindergarten (4K) in 2011-12. Beginning in the 2021-2022 school year, MMSD began phasing in full-day 4K at select schools across the district. The Madison Education Partnership (MEP), in collaboration with the MMSD Departments of Early Learning and Research & Innovation, conducted an evaluation of the program to understand how enrolling in full-day 4K affects student learning relative to half-day 4K. In addition to assessing gains in achievement over the course of the year, we observed in classrooms and interviewed teachers to examine qualitative differences in instruction, time use, and culturally responsive practices across full- and half-day classrooms. Results from the qualitative analysis will be discussed in an upcoming report. (author abstract)