Chapter 3: This study investigated the effects of a new, Spanish two-way immersion program on first through third grade students' English and Spanish proficiency. All students were from an urban, high-poverty community in the Midwest that is English dominant, in a predominantly Anglo state. English-speakers in the two-way immersion program score significantly higher than English speakers in an all-English program on a standardized measure of English language proficiency, while Spanish speakers in the two-way immersion score significantly higher than Spanish speakers in the all-English program on a standardized measure of Spanish proficiency. English proficiency was virtually the same across the Spanish-speaking subgroups in the two-way immersion and all-English programs. A correlation analysis of all students' Spanish-language and English-language proficiency scores revealed that only the two-way immersion Spanish-speaking students' scores on both measures were significantly related. Although sample sizes were relatively small for some subgroups, the initial results are promising regarding the benefits of two-way immersion to English speakers, and the positive relationship obtained across languages for Spanish speakers enrolled in the two-way immersion program. Chapter 4: Researchers have investigated and discussed the advantages and disadvantages of learning and knowing more than one language for decades. Does developing proficiency in two languages truly impact students' thinking, and consequently their performance on academic measures? In this article, the results from a research study on second and third grade students enrolled in a two-way immersion (TWI) program in a large, urban elementary school in a small Midwestern city are presented and discussed. Overall, language-majority students in the two-way immersion program significantly outperformed similar students in a control school on norm-referenced, academic measures of reading and mathematics. Language-minority students, in this case, Hispanic Spanish speakers, scored slightly higher than Hispanic Spanish-speaking peers, but the differences were not significant. The correlations, however, between Hispanic Spanish speakers' Spanish language proficiency and of their reading and mathematics scores were significant in the TWI program. There were no significant correlations between Spanish language proficiency scores and reading and mathematics scores for any other student subgroup. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]