Inspired by Life History Theory, studies have found support for a link between pubertal timing and self-regulation in low-resource environments. This link could potentially explain a link between pubertal timing and early risk behavior. This study builds on this body of research by examining the mediated effect of pubertal timing on sexual activity through self-regulation in adolescents in a group with poor resources and a group with adequate resources. The sample consisted of 728 adolescents and their families. Income-to-Needs (ITN) was measured at age 4 and 7.5 to establish two groups (low-ITN and Medium/High-ITN). Pubertal timing was measured at age 10.5, self-regulation was assessed at age 14 and operationalized with effortful control, and sexual activity was assessed at age 16. Structural equation modeling was employed to test the hypothesized model in both groups. The link between pubertal timing and sexual activity mediated by effortful control was found to be significant but only in the poor-resource group (i.e., low-ITN). Specifically, more advanced pubertal maturity was associated with lower levels of adolescent effortful control, which in turn was associated with more sexual activity at age 16. Findings were partially replicated with a drug use index replacing sexual activity. As this study shows a different operating link from more advanced pubertal timing to effortful control and subsequent risk behavior in resource-poor environments, potential implications for prevention programs are discussed.