The aim of this study was to determine the associations between changes in self-reported toothbrushing frequency and the knowledge and attitudes related to oral health. The study population consisted of all fifth and sixth graders who started the 2001-2002 school year in Pori (n = 1,691); of these, 1,362 were monitored throughout the 3.4-yr study. Data were gathered by questionnaires before, in the middle, and after the follow-up, which was divided into two periods. Associations between changes in toothbrushing frequency, sum score of knowledge items, and sum scores of items in attitudinal factors were studied. The attitudinal factor structure was determined by principal component analyses. The associations were evaluated using mean values and general linear models for repeated measures. Toothbrushing frequency and knowledge and attitudes related to oral health improved among the same children during the study, with the changes usually taking place in the same time-period. In different time-periods, different children's toothbrushing and oral health-related knowledge and attitudes improved. Based on our results, changes in knowledge, attitudes, and behavior are related, but children are ready for change at different times. Therefore, oral health promotion should be designed to be a continuous process rather than a short-term intervention.