The purpose of this study was to determine the effectiveness of doubling the laboratory experiments and time in the laboratory on student achievement, performance on laboratory skills, and attitude toward high school chemistry. One hundred forty-three students were assigned either of two treatments. All students performed the same basic experiments. Students in the experimental group performed, on a weekly basis, an additional experiment related to the basic experiment. All students took the same posttests: CHEM Study midsemester test, investigator's laboratory performance test, and an attitude survey. Among the findings were: no significant difference in the adjusted means of the achievement scores of the experimental and control groups, no significant difference in the attitudes of the groups, and a significant difference in laboratory skills of the experimental as compared to the control group. (Author/CP)