This research brief describes the findings of a study to determine which of the High Schools That Work (HSTW) practices appear to be most effective in raising student achievement. The study explored the effects of six clusters of practices: (1) curriculum standards; (2) academic and career/technical integration; (3) teacher practices; (4) instructional goals; (5) guidance counseling of students; and (6) work-based learning. The analysis incorporated data from test scores and surveys from the 1996 and 1998 HSTW assessments of 424 schools involved in the program. Following are some of the key findings. The career-oriented high school graduates gained in achievement as more of them committed to a solid academic core, even after controlling for socioeconomic and racial variables. On average, schools raised the proportion of students completing the recommended mathematics curriculum by 16 points and the science curriculum by 17 points. Aggregating student scores and other information at the school level, on average, there was a gain in achievement of 13 points in math, 9 points in science, and 4 points in reading. Work-based learning, measured by internship participation and the use of outside experts to review student work, appeared to have a negative effect on achievement, especially in mathematics. (WFA)