Recognizing the underrepresentation and poor academic performance of Mexican American students in mathematics- and science-based fields, the guide (1) reviews student- and institution-related factors contributing to mathematics and science declines, (2), describes selective secondary and college mathematics and science model programs, (3) identifies and describes organizational components of mathematics and science models, and (4) identifies key elements which contribute to successful models. Poverty, poor high school achievement, lack of encouragement, and poor math and science facilities and materials are identified as barriers to Mexican American participation. The models described are available for replication and target precollege students (11 models), community college students (1 model), and four-year college students (2 models). Key elements and organizational components of successful mathematics and science program models discussed include school/college mission, math/science departmental policies and objectives, organizational design, program staffing, type and level of students targeted, curriculum focus, program funding, program evaluation, and student outcomes. The guide includes how-to-do-it suggestions for planning, organizing, and staffing mathematics models. Practical recommendations suggest ways teachers, counselors, administrators, and parents can facilitate the implementation of mathematics and science models and encourage Mexican American students to develop interest in these fields. (NEC)