The purpose of this analysis was to define norms for grammatical morpheme development in Spanish for Spanish-English bilingual children ages 4;0-7;6. This study uses secondary data analysis based on two existing datasets. Participants included 334 Spanish-English bilingual children that were recruited from school districts in Texas, Utah, and Pennsylvania. Grammatical morpheme accuracy was determined by performance on the BESA (Bilingual English Spanish Assessment) (Peña, Gutiérrez-Clellen et al., in preparation). Mean length of utterance in words (MLUw) data was collected from language samples. The average percent accuracy of grammatical morphemes was calculated and analyzed as a function of MLUw in Spanish. Results show that the percentage of accurately produced morphemes has a general upward trend as MLUw increases. Clinical and research implications are discussed.