It has been argued that children learning a second language (L2) omit agreement inflection because of communication demands. The conclusion of these studies is that L2 children know the morphological and syntactic properties of agreement inflection, but sometimes insert an inflectional default form (i.e., the bare verb) in production. The present study focuses on factors that explain errors with subject-verb agreement in the speech of children learning Dutch as their L2. Analyses of experimentally obtained production data from 4- to 9-year-old L2 children reveal that verb form, sentence position, home language, and L2 proficiency determine accuracy with subject-verb agreement in the L2. Most errors were omissions of inflection, in line with the above hypothesis. However, in more exceptional contexts, the children also substituted verb forms, which is more difficult to reconcile with the claim that L2 children's errors reflect insertion of a default form.