Spanish-speaking language-minority (LM) children are at an elevated risk of struggling academically and display signs of that risk during early childhood. Therefore, high-quality research is needed to identify instructional techniques that promote the school readiness of Spanish-speaking LM children. The primary purpose of this study was to evaluate the effectiveness of an intervention that utilized an experimental curriculum and two professional development models for the development of English and Spanish early literacy skills among LM children. We also evaluated whether LM children's proficiency in one language moderated the effect of the intervention on early literacy skills in the other language, as well as whether the intervention was differentially effective for LM and monolingual English-speaking children. Five hundred twenty-six Spanish-speaking LM children and 447 monolingual English-speaking children enrolled in 26 preschool centers in Los Angeles, CA participated in this study. Results indicated that the intervention was effective for improving LM children's code-related but not language-related English early literacy skills. There were no effects of the intervention on children's Spanish early literacy skills. Proficiency in Spanish did not moderate the effect of the intervention for any English early literacy outcomes; however, proficiency in English significantly moderated the effect of the intervention for Spanish oral language skills, such that the effect of the intervention was stronger for children with higher proficiency in English than it was for children with lower proficiency in English. In general, there were not differential effects of the intervention for LM and monolingual children. Taken together, these findings indicate that high-quality, evidence-based instruction can improve the early literacy skills of LM children and that the same instructional techniques are effective for enhancing the early literacy skills of LM and monolingual children. (author abstract)