North Carolina policymakers are interested in which screening and monitoring assessment scores in grades K-3 best predict reading proficiency at the end of grade 3 in order to help educators identify at-risk students, place them in interventions, and monitor their progress. Since 2013, the state has routinely administered screening and monitoring assessments, but the percentage of students scoring proficient in reading at the end of grade 3 has remained largely unchanged. This study used longitudinal student achievement data, provided by the North Carolina Department of Public Instruction, and classification and regression tree analysis to examine how well assessment scores from five points in time in grades K-3 predicted proficiency status on the state reading assessment at the end of grade 3. The score from only one of the assessments identified more than 80 percent of students who scored below proficient at the end of grade 3 as at risk and thus adequately identified at-risk students: the North Carolina Beginning-of-Grade 3 English Language Arts/Reading Test. That state-developed assessment measures the same content standards at the same difficulty level as the state reading assessment at the end of grade 3. The results suggest that more information is needed in order to use assessment data from grades K-2 to reliably identify students at risk of not achieving reading proficiency at the end of grade 3. Educators might want to consider supplementing screening and progress monitoring assessments with informal, curriculum-based assessments that measure student vocabulary, syntax, and listening comprehension skills because research has identified those skills as important predictors of reading comprehension. [For the study snapshot "Identifying North Carolina Students at Risk of Scoring below Proficient in Reading at the End of Grade 3. Study Snapshot. REL 2020-030," see ED607258. For the appendix "Identifying North Carolina Students at Risk of Scoring below Proficient in Reading at the End of Grade 3. Appendix. REL 2020-030," see ED607257.]