Purpose: To assess the impact of a school-based toothbrushing intervention aimed at encouraging primary school children to brush their teeth daily at school, on cognitions, toothbrushing behaviour and habit strength. Design/methodology/approach: The effects of an intervention were examined in a quasi-experimental trial among 296 fifth-graders in seven schools. The schools were randomly assigned to be an intervention group or a control group. Children in the intervention schools brushed their teeth at school under supervision. Effects on toothbrushing behaviour were assessed with written questionnaires before, during, immediately after, and one year after the intervention period. Effects on cognitions and habit strength were assessed one year after the intervention period. Analyses of variance were conducted to detect differences in frequency of toothbrushing, cognitions about toothbrushing, and habit strength. Findings: During the intervention period, brushing teeth at school resulted in a significant increase in frequency of toothbrushing. However, these effects had not been maintained at one-year follow-up. No effects on cognitions about toothbrushing or on habit strength were found. Research limitations/implications: When supports that facilitate healthy behaviour are implemented we recommend evaluating effects on habit strength, by assessment both before and after the intervention. Originality/value: This paper suggests that when habit-inducing supports and cues cease then people find it hard to sustain change. This may be of importance when designing and evaluating health-promoting interventions. (Contains 1 table.)