To what extent do Spanish-speaking English learner students develop English proficiency and grade-level readiness in English language arts and math from early elementary school to upper elementary school? Is there a relationship between proficiency in a student's primary home language, Spanish, and the amount of time needed to attain fluency in the student's second language, English? And are there differences in these relationships across English learner student subgroups? These topics are of high priority to members of the New Mexico Achievement Gap Research Alliance. New Mexico has a long history of working to support the maintenance and development of students' biliteracy skills. Many members of the alliance provide districts with technical assistance related to English learner students, so answers to these questions may inform this technical assistance. This study, conducted by the Regional Educational Laboratory Southwest, sought to inform the New Mexico Achievement Gap Research Alliance about the path toward English proficiency and academic outcomes for Spanish-speaking English learner students who entered kindergarten with varying levels of Spanish proficiency. The study followed two cohorts of Spanish-speaking English learner students in four districts in New Mexico from kindergarten through grade 4 or 5. The 2010 cohort included students enrolled in kindergarten in 2009/10 who were followed through grade 5, and the 2011 cohort included students enrolled in kindergarten in 2010/11 who were followed through grade 4. The study examined cumulative rates of English learner students' progress toward reclassification as fluent English proficient. The study also examined students' demonstration of grade-level readiness on the New Mexico Partnership for Assessment of Readiness for College and Careers (NMPARCC) standardized academic assessments in English language arts and math in grades 4 and 5. All of the results were also observed through the lens of initial Spanish proficiency in kindergarten to understand differences among groups of English learner students. The main findings were: (1) More than 80 percent of English learner students in the 2010 cohort started kindergarten at the lowest English proficiency level, as did half of those in the 2011 cohort; (2) Nearly 83 percent of students in the 2010 cohort attained English proficiency by grade 5, and 59 percent of students in the 2011 cohort did so by grade 4; (3) Among English learner students with high initial Spanish proficiency, nearly all those in the 2010 cohort were reclassified as fluent English proficient by grade 5, and nearly three-quarters of those in the 2011 cohort were reclassified by grade 4; (4) Among English learner students with low or medium initial Spanish proficiency, roughly a quarter of the 2010 cohort were not reclassified as fluent English proficient by grade 5, and almost half the 2011 cohort were not reclassified by grade 4; (5) Of English learner students who were reclassified as fluent English proficient by grade 4 or 5, fewer than a quarter also demonstrated grade-level readiness in grade 4 or grade 5 English language arts or math on the NMPARCC assessment; (6) Regardless of initial Spanish proficiency, the rates of grade-level readiness were generally low on NMPARCC English language arts and math outcomes in grades 4 and 5. However, students with high initial Spanish proficiency were more likely to demonstrate grade-level readiness than were students in the other Spanish proficiency groups; and (7) Grade-level readiness in English language arts and math among students in the two cohorts who were reclassified as fluent English proficient in grades 4 and 5 was generally lower than statewide averages for all students in the same grades in New Mexico. Most students who were identified as English learner students in kindergarten required a minimum of three to four years of instruction after kindergarten to attain English proficiency. A large percentage of students were not reclassified as fluent English proficient before leaving elementary school. Even when students were reclassified, this milestone did not always translate into grade-level readiness in English language arts and math. Among English learner students who were reclassified as fluent English proficient by grade 4 or 5, only a small percentage demonstrated grade-level readiness in grade 4 or grade 5 English language arts and math. The findings suggest that English learner students with low and medium initial Spanish proficiency will not fare as well in English language arts and math as students with high initial Spanish proficiency. A Spanish proficiency measure could be used as an early indicator to target students with low and medium Spanish proficiency in kindergarten for language and literacy interventions in early grades.