More than half of North Carolina's grade 3 students struggle with reading. The percentage of students scoring below proficient in reading at the end of grade 3 was 55 percent in 2017/18. That percentage has remained largely unchanged, at above 50 percent, since 2013/14, when North Carolina passed its K-3 Read to Achieve literacy act. Read to Achieve required North Carolina schools to use interim assessments of reading proficiency in kindergarten- grade 3 to identify students at risk of not achieving reading proficiency at the end of grade 3. Districts administered screening and progress monitoring assessments at the beginning, in the middle, and end of each school year. This study used longitudinal student achievement data for 2014/15-2017/18 and classification and regression tree analysis to examine how well scores on these interim assessments and the North Carolina Beginning-of-Grade 3 English Language Arts/Reading Test (the BOG3 assessment, a state assessment administered separately at the beginning of grade 3) predicted proficiency status on the state reading assessment at the end of grade 3. This appendix provides details on the study sample and the classification and regression tree (CART) analyses used in the study. [For the full study "Identifying North Carolina Students at Risk of Scoring below Proficient in Reading at the End of Grade 3. REL 2020-030," see ED607256. 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.]