Dual-immersion classrooms aren’t just joyful to watch. They’re also ever more important to understand as their approach grows in popularity across the country. But there are some indications that multilingual schools’ increasing appeal is inadvertently undermining the original purpose for the model.

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Dual-immersion programs seem like an answer to a range of difficult questions in education. For instance: How should U.S. schools educate their rapidly growing population of students who speak a language other than English at home? How can districts with shifting demographics simultaneously meet the needs of all of their students? How can schools prepare students for a complicated global economy (and convince families that they’re doing so)?

Research suggests that linguistically integrated dual-immersion programs work best for ELs. These “two-way” programs enroll roughly equal numbers of native English speakers and native speakers of the other language. And, of course, immersion programs offer the perk of multilingualism to all students regardless of what languages they speak at home.

It’s no wonder that new immersion programs are popping up faster than anyone can count (literally: there’s no up-to-date tally of the number of programs in the United States). In the past decade, Utah’s dual-immersion initiative covers around 200 schools. Delaware has a similar statewide program. Portland Public Schools in Oregon has doubled the size of its dual-immersion programs to more than 5,000 students in the past eight years, with those classrooms instructing in a combination of English and Spanish, Mandarin, Vietnamese, Russian, or Japanese. New York City recently launched dozens of new dual-immersion programs across a host of languages.

“We have an incredible wealth, a resource that comes into our country … [this] linguistic and cultural wealth and capital,” Michael Bacon, who oversees the dual-immersion programs in Portland, told me. “If we really, truly are reflective about our history and our country, if we want to stop the systems of repression, if we want to uplift our people and uplift our country, then I think [dual-immersion] is one of the best investments that any community, that any school system, can make.”

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This isn’t a sui generis moment in U.S. language education. Multilingual instruction has a long history in American public schools. In the 19th and 20th centuries, immigrant communities speaking German, Italian, Spanish, Polish, Dutch, or other languages pushed, at various times, for their children to continue learning their parents’ native tongues even as they learn English.

English-speaking Americans’ discomfort with multilingual schools has a similarly long history. Various political pressures—anti-German sentiment during the World Wars, for example—chipped away at these programs over the years. In the 1990s, English-only advocates enacted mandates that largely eliminated bilingual education in California, Arizona, Massachusetts, and in districts around the country. Most of these were Spanish-English programs, which came under scrutiny as part of broader American anxiety about the unity of the country’s identity. Samuel P. Huntington, a political-science professor at Harvard, captured the mood in his 2004 book Who Are We? The Challenges to America’s National Identity, warning, “Spanish is joining the language of Washington, Jefferson, Lincoln, Roosevelts, and Kennedys as the language of America. If this trend continues, the cultural division between Hispanics and Anglos will soon replace the racial division between blacks and whites as the most serious cleavage in American society.”