The use of curriculum-based measurement (CBM) is supported by several decades of research regarding their technical adequacy, practical utility, and use with diverse populations. Questions remain regarding the measurement of growth using tri-annual reading CBM (R-CBM) assessment. Existing research on annual rates of growth is inconclusive with some studies suggesting that the most growth occurs from the fall to the winter and others finding growth accelerates from winter to spring. With a sample of students in third through fifth grades, consisting of a high percentage of English Language Learners (ELLs) and students exited from bilingual instruction, this study found that Non-ELL students demonstrated semester differences in R-CBM growth consistent with prior research in third and fourth grades, but not in fifth grade. However, this pattern was not always consistent for ELLs and students recently exited from bilingual instruction, suggesting that conclusions regarding semester differences in R-CBM growth rates should not be consistently extended to ELLs. (Contains 3 figures and 2 tables.)