Income-based childcare programs provide children access to developmentally appropriate and vocabulary-rich literacy experiences. For this study, participating U.S. Head Start Centers requested families complete a weekly home literacy log to encourage vocabulary-rich shared book reading activities in the home. Using participant characteristics, including literacy log competition, this study examined which factors adequately predicted vocabulary growth as measured by Peabody Picture Vocabulary Test-Fourth Edition standard scores. Results indicated that vocabulary increased significantly for children who were enrolled in participating Head Start pre-kindergarten (Pre-K) programs. Important predictors of the magnitude of vocabulary growth during an academic year included sex, language(s) spoken in the home, and completion of home literacy logs. Clinical implications of this study would warrant recommending home literacy logs as a component of holistic Head Start programming, as completion of literacy logs emerged as an important variable in predicting the magnitude of vocabulary growth second only to race and sex.