The Study That Changed Everything
In the 1980s, researchers Wayne Thomas and Virginia Collier began tracking more than 210,000 students across multiple U.S. school districts. Their mission: find out which educational program worked best for English Language Learners. Thirty years later, their answer was unambiguous.
Dual language programs — and only dual language programs — produced students who fully closed the achievement gap with native English speakers. Every other model they studied (ESL pull-out, transitional bilingual, structured English immersion) left students behind by middle school.
This is not a small study on a small sample. This is the largest longitudinal study ever conducted in American education. And teachers deserve to know what it found.
What "Closing the Achievement Gap" Actually Means
When researchers talk about the achievement gap, they mean the persistent difference in test scores between English Language Learners and native English-speaking peers. In most program models, this gap narrows slightly in early grades, then widens again by middle school as academic content becomes more demanding.
In dual language programs, something different happens. Students spend Kindergarten and 1st grade slightly behind — which is expected, as they are developing literacy in two languages simultaneously. By 3rd grade, they reach parity with native English-speaking peers. By 5th and 6th grade, they begin to *surpass* them — often by 15 to 20 percentile points in both reading and math.
And this advantage grows. The longer students stay in a dual language program, the stronger their outcomes become.
Why Does Dual Language Work When Other Programs Don't?
1. It develops the whole brain.
Research by cognitive scientist Dr. Ellen Bialystok at York University shows that bilingual individuals consistently outperform monolingual peers on tasks requiring attention, task-switching, and working memory — skills that are foundational for academic learning across all subjects.
Managing two languages is constant mental exercise. The brain builds executive function the same way a muscle builds strength.
2. It preserves the home language.
Transitional bilingual programs phase out the home language as English develops. ESL programs barely acknowledge it exists. Dual language does something radically different: it treats the home language as an asset, not a problem to be remediated.
This matters for more than cultural reasons. Dr. Jim Cummins at the University of Toronto demonstrated that academic skills transfer across languages. A student with strong literacy in Spanish develops English literacy faster than a student who never developed home language literacy at all. Subtractive programs that eliminate Spanish are actively sabotaging English development.
3. It creates an additive environment for all students.
In a dual language classroom, both languages have status. Native English speakers learn to read and write in Spanish. Native Spanish speakers gain English. Neither group is labeled "less than." This creates a fundamentally different social dynamic — one where diversity is an academic advantage, not a remediation challenge.
The Question Schools Need to Answer
If the research is this clear, why are dual language programs still the exception rather than the rule?
Part of the answer is resources — dual language requires certified teachers in both languages, and that pipeline takes time to build. Part of the answer is political — in some communities, there is still resistance to non-English instruction, despite thirty years of evidence that it produces stronger English speakers.
But part of the answer is simply that most school leaders and teachers have never seen this research. They were trained in a world where ESL pull-out was "the way we do it" — and they've never been shown a better option.
That is exactly what OurTeachingWorld exists to change.
What You Can Do Right Now
1. Share this research with your principal and district curriculum director.
2. Explore the pillars of dual language education — they apply even in schools not yet running a full dual language program.
3. Visit OurReadingWorld.com to see dual language Science of Reading content in action for Grades 1–5.
The research is not waiting. Your students aren't either.