The author's research indicates that instructional programs that teach English language learners in English are more effective than programs that provide more instruction in the students' native language. Following the passage of Proposition 227 in California, which outlawed bilingual education as the default assignment for English language learners, the author conducted extensive research in classrooms to determine how schools were handling the switch to more sheltered English immersion. She found that many programs that had been identified as "bilingual education" closely resembled sheltered immersion even before the state mandate. Her previous observations had confirmed this mislabeling in other states. Her research on schools that had dismantled bilingual education showed a small but significant positive effect on reading and math achievement. She concludes that teaching students in English yields benefits, and that a sheltered environment is preferable but not necessary to students' success.