This thesis investigates rule-governed behaviour in children within the practical domain of dental care. Eight experiments were conducted to examine how rules, contingencies, and environmental cues, could be employed by parents to empower six year old children to improve their toothbrushing behaviour. Multiple baseline across subjects designs were employed in each experiment. In order to maximize ecological validity and long-term maintenance of behaviour change, (i) all observations were conducted in subjects' homes, (ii) behaviour was recorded by video cameras, and (iii) parents administered the interventions. Experiments 1 and 2 examined the effectiveness of a 'correspondence training' and a 'compliance training' method, respectively. Both procedures increased considerably the frequency and durations of toothbrushing: no apparent differences were noted in the efficacy of the two procedures during training or follow-up phases. Experiments 3 and 4 investigated the effects of incorporating a stimulus control device into the compliance training procedure. The introduction of this device, which provided visual and auditory guidance for the children, showing where to brush and for how long, led to additional large increases in (i) children's durations of toothbrushing, and (ii) the number of locations (tooth surfaces) brushed. Experiments 5 and 6 examined methods designed to improve maintenance by making the 'natural' consequences of toothbrushing more frequently and immediately apparent to the children. A disclosing agent (erythrosine) revealing plaque on children's teeth was introduced into the procedures, and parents were taught to 'score' dental hygiene. Rewarding increases in hygiene 'scores' led to substantial improvements in toothbrushing, but long-term maintenance was not better than in previous procedures. Experiments 7 and 8 investigated the components of the treatment package, and found that similar effects could be generated with less parental intervention and fewer material rewards. The results showed that employing rules, cues and contingencies can be a very effective means of enabling children to alter their behaviour.