We examine the explanatory weight of child-related and contextual factors on first graders’ achievements in spelling and separation between words. The participants were 215 kindergartners, 113 boys and 102 girls (M = 5 years 4 months, SD = 4 months) from both monolingual and bilingual communities in Spain. They were native speakers of Spanish in the monolingual communities and bilingual Spanish/Catalan or Spanish/Basque speakers in the bilingual communities and had Catalan and Basque, respectively, as the language of instruction. The three languages have shallow orthographies. Children were first examined in kindergarten in a number of literacy related abilities (e.g., knowledge of letters, writing) to detect predictors of spelling and separation between words that were, in turn, evaluated at the end of first grade of elementary school. All the participants were assessed in their language of instruction. The best explanatory models were those including interactions among child-level factors and between these factors and contextual variables. Only knowledge of writing in kindergarten appeared as the common explanatory factor for first graders’ attainments. Attainments in spelling were predicted by children’s level of literacy and knowledge of letters moderated by parent’s education; performance in word separation was predicted by phonological awareness and vocabulary knowledge moderated by parental education. Teaching practices affected spelling performance but not learning to separate between words.