This study described the growth trajectories of 105 children (n = 55 boys) who had just started primary school in New Zealand (NZ). Children were assessed every fourth school week around 1.5 months after starting school, for five sessions on Dynamic Indicators of Basic Early Literacy Skills first sound fluency (FSF), AIMSweb letter sound fluency (LSF), and a newly created NZ word identification fluency (NZWIF-Y1), designed for alignment with beginning reading instruction in NZ. In addition to progress monitoring tasks, children were assessed at school entry and after progress monitoring on literacy-related criterion measures. All three progress monitoring measures were sensitive to growth over the children's first 6 months of school. Cross-sectional time-series analyses indicated that within-child increases in FSF and LSF were associated with increases in NZWIF-Y1, although FSF did not add unique variance when both FSF and LSF were entered as predictors. Furthermore, growth mixture modeling indicated three latent growth trajectories for each indicator (FSF, LSF, NZWIF-Y1, respectively): Class 1 - high initial scores and strong growth over time (72.09%, 55.87%, 22.81%); Class 2 - lower initial scores and moderate growth over time (19.18%, 29.12%, 54.30%); and Class 3 - low initial scores and limited progress over time (8.73%, 15.00%, 22.89%). Criterion measures assessed prior and after progress monitoring were typically associated with latent class membership. Results suggest relative growth in performance on repeated assessment of early literacy and word reading skills in beginning reading instruction distinguishes groups of students with differential skill acquisition.