From 2004/05 to 2014/15, the number of English learner students in bilingual or English as a second language (ESL) programs in Texas increased by 47 percent. In the Houston Independent School District (ISD)--the largest district in Texas and the seventh largest in the United States--30 percent of students are English learner students, and 92 percent of these students have Spanish as their home language. The number of students served by the district in bilingual or ESL programs grew at more than twice the rate of total enrollment during the course of the 2014/15 academic year. As a result, the district has been facing a critical shortage of bilingual-certified teachers. Aware of these challenges, the members of Regional Educational Laboratory (REL) Southwest's English Learners Research Alliance sought to obtain clear and actionable information that districts can use when recruiting teachers and assigning them to schools and classrooms that serve large numbers of English learner students. To respond to the needs of the Alliance, REL Southwest designed this study, which uses data obtained from the Texas Education Agency (TEA) and Houston ISD. The study assesses whether a teacher's certification type--being a certified bilingual teacher or a certified ESL teacher--and route to certification--alternative, post baccalaureate, traditional, or additional exam--correlate with academic growth and growth in English proficiency among English learner students whose home language is Spanish. It assesses 10 cohorts of grade 4 and 9 cohorts of grade 5 of Houston ISD English learner students between 2005/06 and 2014/15.