There is an urgent need for early, proactive HIV/STD education. The scientific literature on HIV/STD prevention suggests that there are several factors that affect and, in some measure, predict high-risk sexual behavior in adolescents. These protective factors include communication, self esteem, self efficacy, decision making, knowledge about sexuality and HIV/AIDS, and social norms. However, research on the link between these protective factors and healthy sexual behavior has focused, almost exclusively, on sexually active adolescents and adults. There is a pressing need to examine whether addressing protective factors at an early age is an age appropriate and effective strategy for early HIV/STD prevention. The purpose of this study is to implement and evaluate a late-elementary school life skills curriculum as an HIV/STD prevention strategy. The curriculum, entitled Yo Quiero, Yo Puedo (I Want/I Love, I Can), was developed by the Mexican Institute for the Study of Family and Population (IMIFAP). The curriculum addresses antecedents to high-risk sexual behavior including communication, self-esteem, self efficacy, decision making, knowledge about sexuality and HIV/AIDS, and social norms. This study aims to: 1) develop a quantitative instrument for a 4-6th grade population that effectively measures changes in protective factors associated with sexual behaviors; 2)-test the hypothesis that a late-elementary school life skills curriculum can have a significant impact on protective factors associated with high risk sexual behavior; and 3) to obtain qualitative measures from teachers and students regarding the implementation and perceived impact of the Yo Quiero, Yo Puedo curriculum in Mexican elementary schools. The study will be a two-phase, longitudinal study. In Phase 1, a quantitative instrument will be developed and tested between two groups of 300 students at 6 elementary schools in the Mexican states of Hidalgo and Campeche. In Phase 2, 144 teachers will be trained in the Yo Quiero, Yo Puedo curriculums for Grades 4-6. 3,360 students from 48 schools will then be followed through Grades 4-6. Quantitative measures developed in Phase 1 will be implemented at the beginning and end of each school year to assess change in protective factors. Qualitative measures will also be used to assess perceived impact and impressions of curriculum among both teachers and students, providing the basis for widespread dissemination among government officials in Mexico.