cceeded in school without a special program and acquired a very high level of English literacy. He had two Marquez11crucial advantages, however, that most limited- English-proficient (LEP) children do not have. First, he grew up in an English-speaking neighborhood in Sacramento, California, and thus got a great deal of informal comprehensible input from classmates. Many LEP children today encounter English only at school; they live in neighborhoods where Spanish prevails. In addition, Rodriguez became a voracious reader, which helped him acquire academic language. Most LEP children have little access to books.Random assignment to treatment and control groups, as in medical experiments, is the highest quality research design because it increases the confidence in the conclusion that any differences between the groups after a period of treatment can be attributed to that Marquez12treatment. The results from the five studies in which subjects were randomly assigned to bilingual and control programs favor bilingual education even more strongly. The estimated benefit of bilingual programs on all test scores in English according to these studies with random assignment is .26 of a standard deviation. The positive effect on reading scores is .41 of a standard deviation among the studies with random assignment. And the improvement in scores measured in Spanish is .92 of a standard deviation in the studies with random assignment to treatment and control groups. All of these estimated benefits of bilingual education from studies with random assignment are extremely unlikely to have been produced by chance. The fact that the studies Marquez13of bilingual programs with random assignment, the highest quality research design, have even stronger results greatly increases the confidence in the conclusion that bilingual education positively affects educational attainment. In sum, the NRC report finds that on average, bilingual education programs are more...
