We developed a methodology, derived from the theoretical literatures on rule-governed behavior and private events, to experimentally investigate the relationship between covert verbal self-regulation and nonverbal behavior. The methodology was designed to assess whether (a) nonverbal behavior was under the control of covert rules and (b) verbal reports of these rules were functionally equivalent to the covert rules that control non-verbal behavior. The research was conducted in the context of teaching shopping skills to persons with mild intellectual disabilities using a self-instruction training format. In Phase 1, 4 participants were successfully taught to perform shopping skills using overt and covert self-instructions. The self-instructions were then blocked under overt and covert self-instruction conditions, which resulted in a reversal of shopping skills to baseline levels. This indicated that the overt and covert self-instructions might be controlling responding. In Phase 2, we demonstrated that the self-instructions, when used as external directives, produced successful shopping with 3 other participants. By demonstrating that self-rules can produce correct responding when used as external directives, we were more confident that it was the self-instructions and not other verbal or nonverbal behavior that controlled responding under overt, covert, and blocking conditions in Phase 1.