This report reviews 75 high schools in the "High Schools that Work" (HSTW) network that made statistically significant gains in at least two of three areas reading, mathematics and science--between 2002 and 2004 on the "HSTW" Assessments. In these schools, all groups of students improved achievement--regardless of race, ethnicity or socioeconomic background. The successes of these schools can be attributed, in large measure, to their vigorous application of the "HSTW" Goals and Key Practices. These most improved schools created a rigorous and relevant curriculum for all students, and bolstered their high expectations with strong relationships. They engaged teachers, parents and guidance counselors to support students in setting goals, planning programs of study to meet the goals and passing tougher courses. Implementation of "HSTW" Design--Items Included in 10 Aspects of the "HSTW" Design, is appended. (Contains 15 tables and 14 figures.) [SREB school improvement and leadership preparation initiatives are supported by state consortia, the Wallace Foundation, the Bill and Melinda Gates Foundation, the Wachovia Foundation, the Charles Stewart Mott Foundation, the Carnegie Corporation, the U.S. Department of Education, and contracts with state and local school districts.]