Purpose: This study aimed to describe change in dual language learners' (DLLs) morphosyntactic skills from kindergarten to first grade based on a sentence repetition task in English and Spanish. Methods: The sample included Spanish-English speaking children (n = 25). Investigators employed a repeated measures analysis of variance with one within-subjects effect (time). Results: Overall there was a significant difference in sentence repetition accuracy between time points showing growth in English (p < 0.001, d = 1.24), and no significant change in Spanish. Results highlight malleable English grammatical forms (e.g. conditional (if-then); question inversion of auxiliaries; and subordinating conjunctions) and forms that remained challenging for DLLs in first grade (e.g. irregular past). Conclusion: Findings support the use of a sentence repetition task as a progress monitoring tool for young DLLs. Highlighted grammatical errors may be informative for planning intensified instructional support in kindergarten and first grade. [For the corresponding grantee submission, see ED588804.]