A study of the relative effectiveness of three approaches to teaching selected aspects of English grammar to 299 10th-grade students of average ability (17 class-size groups) was made in Lane County, Oregon. Five groups were taught using structural linguistics concepts; six groups employed traditional methods, materials, and approaches; and six served as control groups with instruction left to the teacher's discretion. Before instruction, students were equated by test scores, general age, and sex characteristics; and teachers were given inservice training, counselled in the use of instructional materials, and tested for fidelity to their teaching approaches. After a year of grammar instruction, the students were tested again with both standardized and experimental instruments. The major findings ofthe study were that (1) the performance means of the structural-approach groups and the traditional-approach groups did not differ significantly; (2) significant differences at the .01 level were found between the performance means of the undefined approach groups and each of the well-defined structural- and traditional-approach groups; (3) significant differences at the .01 level were found between performance means for boys and girls; (4) none of the approaches improved students' attitudes toward grammar. (Author/LM)