Background: Studies have demonstrated strong predictive and concurrent validity of curriculum-based measures (CBMs) with high-stakes reading tests, mainly using oral reading fluency (ORF) to predict outcomes. Some studies have found that CBMs' predictive accuracy might vary across demographic subgroups of students. In this study, we investigate whether additional CBMs of reading comprehension account for variance beyond ORF and whether these reading variables predict reading comprehension differently for demographic subgroups. Methods: Curriculum-based measures were administered to 9,967 students at the end of Grade 3 in the United States, concurrent with a high-stakes standardised state reading comprehension achievement test (RCAT). Hierarchical regression models with RCAT as the outcome were used to test: (1) whether CBMs of reading comprehension accounted for significant variance beyond ORF; and (2) if the reading variables differentially predicted RCAT for different subgroups of students. Results: Oral reading fluency explained significant variation in RCAT, and the addition of comprehension CBMs accounted for small amounts of unique variance. The contribution of ORF in explaining variation in reading comprehension varied by demographic subgroups. Conclusions: The contributions of comprehension CBMs in predicting high-stakes standardised reading comprehension tests were not meaningful, only accounting for small amounts of unique variance. Additionally, the contribution of ORF in explaining variation in the high-stakes standardised reading comprehension test varied by student demographics, likely due to complex reasons specific to those individual factors.