Early sexual onset contributes to poor health outcomes through the life course. We use the social behavioral model to examine the behaviors and attitudes associated with early sexual onset and the intention to delay sex in middle school youth. Youth in rural communities with high rates of hepatitis C and HIV filled out a survey prior to implementation of an evidence-based sex education program. Participants were asked if they had ever had sex and whether they planned to abstain from sex until the end of high school. We collected demographics, attitudes about abstinence, agency for sexual refusal, parent communication, sexual health knowledge, and history of system involvement. Logistic regression was utilized to examine factors associated with each outcome. Our sample included 6,799 students, 12.7 years old ± 0.9 and 50.3% female. 5.1% had ever had sex and 73.9% planned to abstain until the end of high school. Early sexual onset was associated with older age, negative attitudes toward abstinence, lower agency for sexual refusal, more frequent parent communication about sex, history of child welfare, and history of juvenile involvement. Planning to abstain until the end of high school was associated with being younger, female, positive attitudes toward abstinence, higher agency for sexual refusal, less communication with parents about sex, more communication with parents about relationships, not having a history of foster involvement, and not having a history of juvenile involvement. Age, agency, and parent communication were all associated with both outcomes. Our findings highlight the importance of early comprehensive, trauma-informed sex education.