This study examined how attaining English proficiency and being reclassified as fluent English proficient affected achievement in English language arts and math in the first year after student reclassification in grades 3-8 in New Mexico. State policy in New Mexico bases student reclassification decisions on whether students attain a minimum overall English language proficiency level score of 5.0 on the ACCESS for ELLs (ACCESS) assessment. The study focused on achievement among English learner students in 2014/15-2018/19, a time when the ACCESS underwent a standards setting process to better align its language proficiency scoring scale with the expectations of college- and career-ready standards. After the standards setting, a smaller percentage of English learner students in New Mexico attained English proficiency and were reclassified each year. At the same time, students who scored near the English proficiency level required for reclassification performed above the statewide average in English language arts and math and were more likely to meet state content proficiency standards. However, the study found no effects of reclassification on student achievement either before or after the ACCESS standards setting. In addition, the study found no effect of reclassification on next-year English language arts and math achievement among most groups of students with different characteristics and among most districts in the study. Leaders at the New Mexico Public Education Department could use the findings of this study to consider maintaining the current reclassification threshold. In addition, the state and its districts might want to identify opportunities to strengthen the supports provided to English learner students. This could begin by collecting more systematic information on the education services and supports that English learner students receive leading up to and after they attain English proficiency. [For the Study Snapshot, see ED622076. For the appendixes, see ED622078.]