The Portland study was able to compare students who were randomly assigned to the district's dual-language programs with students who did not receive such instruction.

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A big, new study out of Portland found significant gains in reading for students enrolled in dual-language immersion programs, in which students are taught in both English and a second language.

Portland students enrolled in such programs had reading skills in English that were almost a full year higher than their peers, according to the study, which was released this month.

The study, which included 27,741 children,  found that students randomly assigned to Portland Public Schools’ immersion programs in Spanish, Japanese, Mandarin Chinese and Russian were better readers than students not enrolled in the programs.   The immersion students outperformed other students by about seven months in fifth grade and nine months in eighth grade, the study found.

The study was done by the Rand Corporation, American Councils for International Education and Portland Public Schools, and researchers said the results held for native English speakers as well as those learning English as a second language.

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Non-native English speakers enrolled in a dual-language program also were less likely to be classified as needing English-language instruction by the sixth grade, the study found. The study also found that immersion students reached intermediate levels of proficiency in the new language by eighth grade.

In math and science, the study found no benefit, but also no detriment, for students in the dual-language programs.

“Though effects in mathematics and science are less evident, a program that yields improved reading in English, improved long-term exit rates from EL (English language)  status, no apparent detriment to mathematics and science skills, and promotes proficiency in two languages seems difficult to criticize,” the researchers wrote.

The study adds to a growing body of research that also points to benefits of dual-language instruction.

About 10 percent of Portland students are enrolled in immersion programs, which are offered in a quarter of its schools. The district offers two-way programs, where half of the students are native English speakers and half are native speakers of the other language being taught, and one-way programs, where most students are new to the second language. The district also offers a Vietnamese program, but it wasn’t included in the study.

The fact that the district assigns students to dual-language programs by a random lottery helped researchers examine the differences between the students in dual-language versus standard, one-language education.

In Washington, 30 of the state’s 295 school districts offer dual-language programs. Seattle Public Schools has Spanish-English, Japanese-English and Chinese-English programs; Highline offers programs in Spanish and Vietnamese.

Three new Washington school districts will soon receive $100,000 to establish dual-language immersion programs, the state superintendent’s office announced Monday. Bethel, Selah and Mabton will each establish a Spanish-English program, while Wenatchee and Bellevue will receive grants to expand existing programs and serve as mentors to the new districts.