The following are only a few of several studies that have been done, showing that in statistically controlled studies, Bilingual Education clearly outperforms the English-Only approach.

It is very important to note that these studies are academically motivated and not  politically motivated. The researchers who performed these studies seek to comply with the goals of academic accuracy and quality of research. If they didn't they would  lose  respect in their field. For more commentary (by a world renown expert  in  the linguistic field) about this aspect of educational research in language acquisition please see:
http://ourworld.compuserve.com/homepages/JWCRAWFORD/cummins2.htm
 

Controlled Study - A controlled study is set up to account for all relevant factors, and analysis of data is performed with the powerful techniques developed in the field of statistics. Controlled studies are used in many fields. For example, in the field of medicine controlled study techniques are used to evaluate the efficacy of drugs and other medical procedures. Many lives are saved due to controlled studies. The use of controlled studies to evaluate educational methodology is also well respected and has been used to make many advances in education -- not just in the area of language acquisition but in many other areas as well. 

Statistically Significant - This term is not just a descriptive term. In the field of statistics it means that the difference observed is more than random variation and the comparison meets a rigorous test of statistical validity.

LEP - Limited English Proficient. In Arizona, students who score below an NCE reading score of 43 are considered Limited English Proficient. (Half of all students score an NCE score of 50 or above.)

Bilingual Education - Bilingual programs introduce children to English from day one and the portion of English is increased as time progresses. Academic subjects (e.g. Math, Science, etc.) are taught in the language the student understands best -- which initially is their first language. This is done so that the students don’t get behind in Math, Science, etc. while they are learning English. As soon as a student can comprehend the academic subjects in English, then they are taught those subjects in English from then on.
 

Mortensen (1984) compared grade 4, 5 and 6 Spanish speaking students in two programs, a bilingual program with transitioning to English reading in grade 3, and a monolingual English program. According to Mortensen, subjects in the two programs lived in "close proximity" to each other, and were from a similar socioeconomic background.

Mortensen reported that the bilingual education students did statistically and significantly better on a test of comprehension skills. 

Reference:  Mortensen, E. 1984. “Reading achievement of native Spanish-speaking elementary students in bilingual vs. monolingual programs,” Bilingual Review  11(3): 31-36.
 

de la Garza and Medina (1985) compared children (grades 1-3) in a bilingual program (initially LEP) to English-dominant (non LEP) children in an all-English program -- a very severe test. Initially, eighty percent of the bilingual education children were classified as limited English proficient (LEP), but 94% of the comparisons were English-dominant (already English proficient). For the bilingual group the first language was used 75% of the time in grade 1, 70% in grade 2 and 50% in grade 3.

Children in the bilingual program scored statistically as well as the English-speaking comparison students and even statistically outperformed them in the second grade vocabulary test.

In addition, the socio-economic class of the English speaking children may have been higher.

Reference:  de la Garza, J. and Medina, M. 1985. Academic achievement as influenced by bilingual instruction for Spanish-dominant Mexican-American children. Hispanic Journal of Behavioral Sciences. 7(3): 247-259.
 

Gonzales (1989) compared English reading scores for sixth grade Mexican-American children born in Mexico who had received at least two years of their education in Mexico and Mexican-American children who had received all of their education in the US in English. All children were of low socio-economic status. The Mexican-born children did better on a test of English reading.

This an important result because the the Mexican-educated children had "de facto" bilingual education. That is they had  literacy and subject matter teaching in their own language. This is strong evidence for bilingual education, because these are the components good bilingual programs provide.

Reference:  Gonzales, L. Antonio. 1989. Native language education: The key to English literacy skills. In D. Bixler-Marquez, J. Ornstein-Galacia, and G. Green (eds.), Mexican-American Spanish in its societal and cultural contexts. Rio Grande Series in Languages and Linguistics 3. Brownsville, Texas: University of Texas, Pan American. pp. 209-224.
 

In Appel (1984) Turkish and Moroccan children ages 7 to 12.6 were placed in either bilingual or "regular" classes in Leiden in the Netherlands. The bilingual group had special instruction in Dutch for 20% of the time, and also had all subjects taught in the primary language for the first year, but "as soon as the immigrant children were able to understand and speak some Dutch, they joined Dutch children for a few hours a week.” In the second year, the program was 50% primary language and 50% Dutch, and in year three all instruction was in Dutch. Comparison children had all instruction in Dutch, with 20% of the day in "special instruction."

"The children from the bilingual education group did better on a wide variety of tests of Dutch, and the difference was statistically significant on the test of reading comprehension. 

Appel noted that "In general, it can be concluded that the amount of time on minority-language teaching in the transitional bilingual school ... did not harm or hinder the second language acquisition of the Turkish and Moroccan immigrant workers’ children. At the end of the research period, these children were statistically ahead in oral and written second-language proficiency as compared to children who were instructed entirely or almost entirely in Dutch.”

The impact of bilingual education was apparently not limited to language: "In the first three school years the mean percentage of ‘problem children’ in the (regular) group was nearly twice as high as in the (bilingual) group (24% vs. 13%). Social-emotional problems were exhibited in aggressive behavior, apathy ..."

Reference:  Appel, R. 1984. Immigrant Children Learning Dutch..Dordrecht, The Netherlands: Foris.
 

A study by Saldate, Mishra and Medina (1985) compared bilingual education and English-only programs in Douglas, Arizona, a city on the Mexican border in which a great deal of Spanish is spoken.

For the bilingual education group, the first language was used 90% of the time in grade 1, 80% in grade 2, and 50% in grade 3. Also, by grade 3, alternate-day instruction was introduced for subject-matter teaching.

Children were tested at the end of grade 3 on the Wide Range Achievement Tests (WRAT). For the WRAT, scores for English reading are presented here, a test that emphasizes word recognition and decoding. At the end of the study in grade 3, the bilingual education students statistically outperformed the English-only students

Here the difference was statistically significant and quite large.

Reference: Medina, M., Saldate, M., and Mishra, S. 1985.The sustaining effects of bilingual education: A follow-up study. Journal of Instructional Psychology 12(3): 132-139.
 

When children are tested during bilingual programs or immediately after they are exited, bilingual education shows a clear advantage. In Arizona, results for the highest grade for Saldate et. al (1985). are quite positive and statistically significant, and de la Garza and Medina (1985) show that bilingual education students (starting as LEP) do as well or better than English-dominant (non LEP) students.

These results do not support the view that bilingual education in Arizona is a failure. In fact, Arizona studies strongly suggest that bilingual education is beneficial, a conclusion that is consistent with the results of studies done in other states. What is clear is that calls for the elimination of bilingual education are completely unjustified.

The results presented here probably underestimate the positive effects of bilingual education. Some of the details provided by those implementing the bilingual programs suggest that the programs were not set up in an optimal way (Krashen, S. 1996. Under Attack: The Case Against Bilingual Education. Culver City, CA: Language Education Associates ). One would expect that bilingual programs that are better implemented would produce even stronger results. We have learned a great deal since the 1970s and 1980s.

The above summaries of statistically controlled studies on bilingual education are based on the reviews published by the following:

Krashen, S., University of California, Bilingual Education: Ninety Questions, Ninety Answers, (http://www.alec2000.org/ninety.htm)

Krashen, S., Park, G.K. (University of California), G.K., Seldin, D. (University of California, Riverside), Bilingual Education in Arizona: What the Research Says, September 1, 2000, (http://www.alec2000.org/research2.htm)
 

Appel, R. 1984. Immigrant Children Learning Dutch..Dordrecht, The Netherlands: Foris.

de la Garza, J. and Medina, M. 1985. "Academic achievement as influenced by bilingual instruction for Spanish-dominant Mexican-American children". Hispanic Journal of Behavioral Sciences. 7(3): 247-259.

Gonzales, L. Antonio. 1989. Native language education: The key to English literacy skills. In D. Bixler-Marquez, J. Ornstein-Galacia, and G. Green (eds.), Mexican-American Spanish in its societal and cultural contexts. Rio Grande Series in Languages and Linguistics 3. Brownsville, Texas: University of Texas, Pan American. pp. 209-224.

Krashen, S. 1996. Under Attack: The Case Against Bilingual Education. Culver City, CA: Language Education Associates

Krashen, S., University of California, Bilingual Education: Ninety Questions, Ninety Answers, (http://www.alec2000.org/ninety.htm)

Krashen, S., Park, G.K. (University of California), G.K., Seldin, D. (University of California, Riverside), Bilingual Education in Arizona: What the Research Says, September 1, 2000, (http://www.alec2000.org/research2.htm)

Medina, M., Saldate, M., and Mishra, S. 1985."The sustaining effects of bilingual education: A follow-up study." Journal of Instructional Psychology 12(3): 132-139.

Mortensen, E. 1984. “Reading achievement of native Spanish-speaking elementary students in bilingual vs. monolingual programs,” Bilingual Review  11(3): 31-36.