The study examined how the English reading performance of predominantly Spanish-speaking students in transitional bilingual education compared with the performance of predominantly Spanish-speaking students in structured English immersion. The study analyzed data on three cohorts of students in six schools in Los Angeles; Denver; Albuquerque; St. Paul, MN; Rockford, IL; and Alamo, TX, from 2004 to 2009. Students were randomly assigned to receive either transitional bilingual education or structured English immersion upon entering kindergarten and were followed for three, four, or five years. Proficiency in English reading was measured using standardized tests administered at the end of each year. The study compared test scores of students in the transitional bilingual education group with those of students in the structured English immersion group. Scores on four English tests were examined. At the end of kindergarten and first grade, students in structured English immersion had significantly better English-reading skills than students in transitional bilingual education. The WWC interprets these effects as corresponding roughly to the skill difference between the 50th and 66th percentiles of English reading achievement. By the end of second and third grades, when many students in transitional bilingual education had switched to instruction in English, the differences in skills were statistically insignificant for six of the eight outcomes. When the students reached fourth grade, they only received English instruction. At this time, differences in English-reading skills between the groups were all statistically insignificant. Two of the four outcomes, though, showed large enough differences favoring structured English immersion that the WWC considered them noteworthy: the effect sizes were roughly equivalent to the skill difference between the 50th and 61st percentiles of English reading achievement. The research described in this report meets WWC evidence standards and is a well-implemented randomized controlled trial. (Contains 3 footnotes.) [The following study is the focus of this "Quick Review": Slavin, R. E., Madden, N., Calderon, M., Chamberlain, A., & Hennessy, M. (2010). "Reading and language outcomes of a five-year randomized evaluation of transitional bilingual education." Baltimore, MD: Johns Hopkins University.]