The "Effects of Reclassifying English Learner Students on Student Achievement in New Mexico" study examined being reclassified as fluent English proficient and achievement in English language arts and math in the first year after student reclassification. The study focused on achievement among English learner students in 2014/15-2018/19 in New Mexico. The New Mexico Public Education Department provided student-level administrative data on student English language proficiency, student English language arts and math achievement, and demographic characteristics through a data-sharing agreement with the Regional Educational Laboratory Southwest. This document presents the following three appendixes that accompany the study: (1) Methods; (2) Supporting tables; and (3) Supplemental analyses. [For the full report, see ED622075. For the Study Snapshot, see ED622076.]