The purpose of this study was to implement a professional development program for kindergarten teachers and to evaluate its effect on the quality of early literacy at the classroom level and on preschool children's learning. An experimental design with randomized selection and assignment and pre- and post-test measurements was used. The sample consisted of 48 kindergarten teachers and 240 pre-kindergarten and kindergarten children.The initial quality of the classrooms was assessed by applying the Early Literacy and Language Observation Inventory (Smith and Dickinson, 2002). Oral language, phonological processing and print knowledge were measured with the Early Literacy Test (Villalon and Rolla, 1999) and the Test of Vocabulary in Pictures (TEVI-R) (Echeverria, Herrera and Segure, 2009). The intervention consisted of a literacy seminar and direct coaching to the educators of the treatment group, during six months, with the purpose of helping them improve their pedagogical practices, addressing the skills that international research has highlighted as relevant and predictors of reading and writing acquisition: oral language, phonological processing and print awareness. The results show positive changes in six measures of quality (ELLCO-Pre K) global, language, print knowledge and literacy with high effect sizes; however, no significant impact on children's literacy learning was observed. It is concluded that it is necessary to generate more efficient instructional strategies that account for a longer maturation time to produce effects in children.