This study examined teachers' implementation of an early literacy intervention, Systematic and Engaging Early Literacy (SEEL), on kindergarten children's development of early literacy skills. One hundred forty-nine kindergarten children (102 treatment) across six classrooms participated in this study. Results reveal that children who received SEEL instruction evidenced greater learning outcomes in relation to children in the comparison group on rhyme awareness, rhyme generation, letter knowledge, and letter-sound association but not on spelling, blending, or reading tasks. Results also reveal that children with limited phonological skills benefited most from the intervention, in that they made significantly greater gains in literacy skills than children with more proficient phonological skills. Results are examined with attention to teachers' fidelity of SEEL implementation. Findings are discussed in relation to the important role that intervention fidelity has on teachers' implementation of systematic and engaging instruction and its effect on children's letter knowledge and phonological awareness development.