The study took place in an urban area in the Rust Belt region of the United States. A total of 28 Head Start classrooms from 12 schools were included in the study. The 28 classrooms were split evenly between full-day and half-day instruction.
The researchers randomly assigned 6 Head Start centers to the intervention group and 6 Head Start centers to the comparison group. Classrooms within the assigned centers were then stratified based on half-day and full-day instruction, and a random sample of these classrooms were selected for inclusion in the study. A total of 460 students in preschool were included in the study. The 460 preschool students were taught by 28 teachers in 12 schools. Fifty-three percent of the students were female, 96% spoke English as their primary language at home, and all were eligible for free- or reduced-price lunch. Fifty percent were Black, 25% were White, 9% were Asian, 10% were two or more races, and 6% were another race or unknown. Approximately 1% of the students were Hispanic.
World of Words (WOW) is a 24-week supplemental curriculum designed to support children's vocabulary acquisition and conceptual knowledge development. The curriculum was organized into three units, each 8 weeks long, that covered healthy habits, living things, and mathematical concepts. Each unit included four topics, which represented a component of the specific unit. For example, the healthy habits unit included topics focusing on emotions and healthy foods, while the living things unit included topics on insects and pets. Each topic within a unit was taught over an 8-day period for 12–15 minutes daily alongside the core curriculum, which was HighScope. In each topic, WOW includes a specific sequence of instructional activities. For example, on day 1, the first lesson focused on a phonological awareness skill (like rhyming); on day 2, in addition to phonological awareness activities, a content video was shown, which introduced students to the topic (for example, what an insect is, in the living things unit). On subsequent days, additional scaffolding activities were incorporated, including book reading, displaying in-category and out-of-category picture cards (for example, what is and is not an insect), introduction of challenge words, journal-writing, and a final review of the topic. Main concepts and related vocabulary words were introduced and practiced over the course of instruction.
Students in the comparison group Head Start centers received a supplemental vocabulary curriculum, which used materials from the Growing Readers Early Literacy Curriculum (DeBruin-Parecki & Hohmann, 2006). The supplemental curriculum included storybooks and activities in vocabulary, print knowledge, and phonological awareness skills and was taught for 12–15 minutes daily alongside the HighScope core curriculum for three 8-week instructional sessions.
Support for implementation
Teachers in both the WOW and comparison groups received 2 days of professional development training before classes began. The intervention group received training on WOW and the comparison group teachers received training on Growing Readers Early Literacy Curriculum.