The impact of large-scale testing on curriculum policies at district and school levels and on science teaching at the classroom level was studied for British Columbia (Canada). Other factors affecting teaching practices were considered. In 1983, the Province reintroduced centrally set and graded province-wide examinations for grade 12, following a 10-year period without such examinations. The examinations studied were the grade-12 final examinations in secondary science and science assessments conducted in grade 10. Data were collected from teachers and students in grades 8, 10, and 12, and from principals and district and province administrators. Phase 1 data were collected from 24 teachers in 2 districts. Phase 2 data were collected from observations of and interviews with 56 teachers in 10 districts as well as several administrators. At grades 8 and 10, teachers reported little influence of the government examination. At grade 12, the examinations had enormous impact. Objections usually centered around the narrowing of curriculum, the psychological pressures of the examinations, the erosion of creative teaching, and the notion that some aspects of education were being ignored in science teaching. The grade-12 examinations used in British Columbia are not mere indicators of performance. Evidence indicates that these examinations have effectively frozen innovative practices in grade-12 science teaching. Alternatives to the current situation are discussed. Four figures, 2 tables, and 29 references are included. (SLD)