The U.S. educational system generally does not support multilingualism in its curricula; despite their name, bilingual programs are often subtractive in nature, where the goal is to replace the weaker heritage language (HL) with the majority language.  In contrast, additive bilingual programs that use the HL as the medium of instruction show strong research support for effectiveness: lower dropout rates and higher test scores on English and other content areas (Francis, Lesaux, & August, 2006; McCarty, 2014).  However, parents and educators continue to fear that educating bilingual children in the HL will have negative consequences on their English development, and this will hinder their academic performance as compared to their monolingual counterparts.  This paper presents longitudinal data from an additive Spanish immersion preschool to explore what happens when minority language students are educated entirely in the HL in early childhood.  Our research questions are (1) What linguistic gains do children make in a Spanish immersion educational context over time? (2) What effect does enrollment in a Spanish-immersion school have on children’s English development? 

Seventy-four children ages 2 through 8 were recruited for the study.  The data were collected at a Spanish immersion preschool through naturalistic observation, a Spanish story elicitation task, and the preLAS, a standardized assessment available in both English and Spanish.  Findings revealed that one year of enrollment in the school results in a statistically significant increase in the percentage of Spanish in the story elicitation task, p < .001, and significant increase in score on the Spanish preLAS, p =.009.  Notably, results also indicated that students made significant gains in their English as well, as shown on their English preLAS scores over time, p = .019.  Additionally, in comparing these results to previous studies, the children enrolled in the Spanish immersion preschool had higher English scores than age-matched heritage speakers of Spanish enrolled in an English only school.  The study suggests that despite the Spanish immersion environment of the school, children make significant gains in both Spanish and English, dispelling fears by parents and educators of children not making progress in English in immersion preschools.  Implications for early heritage language education will be discussed.