The current study develops and evaluates a tool to distinguish four different categories of educators for the effective delivery of HIV/AIDS health education using data from 548 randomly selected participants aged 16 years. The D4 Diagnostic Quadrant is based on HIV knowledge and sexual practice behaviours and indicates four distinct typologies of educator. The discerning educator has high HIV/AIDS knowledge and healthy sexual practices. The dissolute educator has high HIV/AIDS knowledge but employs unhealthy or risky sexual practices. The decorous educator has low HIV/AIDS knowledge but practices healthy sexual practices. The disempowered educator has low HIV/AIDS knowledge and employs unhealthy or risky sexual practices. The study found that the two categories that will result in the most effective behaviour-change interventions are those that target discerning and decorous individuals as the educators. Both these categories have underlying healthy practices that minimise the risk of HIV transmission. The D4 Diagnostic Quadrant tool provides information as to existing knowledge and beliefs about HIV/AIDS that can inform decisions relating to the allocation of scarce resources. The tool will be very useful in the selection process of would-be educators particularly in health-promotion interventions.