This report describes the Day Care Youth Helper Program (DCYHP) developed at a number of demonstration sites across the country. The program was designed to give high school and junior high school students an opportunity to work with preschool children through field experience in day care centers, coupled with a seminar for the planning of early childhood learning activities and the introduction of child development concepts. Demonstration projects were located in 14 public high schools, one privately funded alternative school and one public junior high school. Sites were selected to represent diverse geographical, socioeconomic, and ethno-cultural groups. The report describes program goals and concepts and the history of the demonstration projects over a 4-year period. Materials developed for use in the program are discussed in detail and a synopsis of evaluative material is included. Report chapters deal with: establishment of demonstration sites; the project director's job and training; materials for students and for supervisors; field experience; the seminar; and program evaluation. Evaluations showed: (1) surprising stability in the impact of the program on students, teachers and institutions; (2) institutionalization of the program in all but two of the original sites; and (3) replication of the model in over 20 sites with only technical assistance and no external funding. Among striking student gains, the successful participation of special students with problem histories was seen as particularly significant. (Author/BF)