Purpose The purpose of this study was to examine the effects of a supplemental Spanish language instruction program for children who spoke Spanish as their native language and were attending English-only preschool programs. Specifically, the study evaluated the program’s effects on the children’s Spanish sentence length in words, subordination index, and grammaticality of sentences. Method Forty-five Spanish-speaking children attending English-only prekindergarten classrooms were selected for study. Of those, 15 children received 30 min of Spanish instruction 5 days a week for 16 weeks. The program targeted 5–10 vocabulary words a week, dialogic book reading, phonemic awareness, and letter knowledge. The remaining 30 children participated in regular preschool English instruction. Students were evaluated before intervention, immediately after intervention, and 4 months following intervention. Results Repeated measures analyses of variance indicated that the children who received the small-group supplemental Spanish language instruction made significant gains in their Spanish sentence length in words and subordination index when compared to those receiving regular English-only classroom instruction. There were no differences in the children’s grammaticality of sentences. Discussion and Clinical Implications The findings demonstrate that a daily short native language program has significant effects on sentence length in words and subordination index in English language learners who are attending English-only preschool programs.