In 1998, California passed Proposition 227, which severely restricted the use of primary language for instructing English learners, calling for a 1-year transitional program of structured English immersion. Researchers examined the effects of Proposition 227 in districts and schools statewide during the first year of implementation. Data from observations and interviews with district administrators, principals, teachers, and bilingual coordinators indicated that statewide, 29 percent of English learners were in primary language programs prior to 227, and 12 percent were in one after implementation of 227. Districts with a history of extensive primary language programs and significant numbers of certified bilingual staff were most likely to continue these programs. Where there was strong district leadership in providing parents with information about alternatives to structured English immersion classes or in urging principals to discontinue primary language instruction, schools followed suit. Teachers exercised considerable autonomy in interpreting district and school directives. There was significant confusion statewide about the school and district roles in informing parents of their rights to seek waivers from structured English immersion programs. What teachers chose to do in their classrooms following 227 depended largely on what they had done prior to 227 and on their own skills, experience, and beliefs about student learning. (Contains 18 references.) (SM)