This study was prompted by the Arizona Department of Education's interest in learning more about the progress of English learner students toward English proficiency in the early grades. The study examined the English language proficiency and English language arts (ELA) proficiency (reading and writing at grade level) of non-native English speaker students in kindergarten and in grade 3. About 11 percent of 2013/14 kindergartners in Arizona were initially classified as English learner students. At the end of that school year, Arizona retested all non-native English speaker kindergartners after setting a higher threshold for English language proficiency. After reassessment, the proportion of kindergartners classified as English learner students rose to 18 percent. Students initially classified as English language proficient and reclassified as English learner students at the end of kindergarten were no more likely to achieve proficiency by the end of grade 3 than were students initially classified at the basic/intermediate (below proficient) level. This finding suggests that students who were reclassified likely needed English learner services at kindergarten entry. One group of students outperformed native English speakers on grade 3 proficiency assessments: non-native English speakers who were proficient when they entered kindergarten and confirmed as proficient when reassessed at the end of the school year. This finding increases confidence that these non-native English speaker students were appropriately classified as not needing English learner services. A small amount of the variation in English language proficiency and ELA proficiency in grade 3 was attributable to school characteristics, but most of the variation in outcomes was attributable to student characteristics. This suggests that practitioners and policymakers might want to investigate how to reduce gaps in achievement within schools in addition to increasing students' achievement levels overall. Student characteristics associated with lower outcomes in grade 3 included lower English language proficiency level at kindergarten entry, being eligible for special education services, being a racial/ethnic minority student, and being male. Being socioeconomically disadvantaged was associated with a lower probability of achieving ELA proficiency by the end of grade 3 but not with reaching English language proficiency. [For the appendixes, see ED607062; for the study snapshot, see ED607063.]