The current study analyzes the relationship between elementary school reading achievement and participation in the following language acquisition programs--transitional bilingual, developmental, two-way bilingual immersion, and English immersion. With a focus on the achievement of Spanish-dominant English learners, the study uses multilevel models to examine Spanish and English reading outcomes for evidence of an "additive advantage" associated with programs that pursue full proficiency in students' home language and English. Set in a large urban school district in Texas, this research finds that participants in the most additive program, two-way, earned the highest Grade 5 English reading performance. In contrast, students in transitional and two-way programs demonstrated similar Spanish reading growth, and developmental students had significantly slower growth than transitional students.