This study aimed to evaluate the impact of dental caries treatment on oral health-related quality of life (OHRQoL) among schoolchildren and the responsiveness of the Child Perceptions Questionnaire (CPQ8–10) instrument. Brazilian schoolchildren, 8–10 yr of age, were randomly selected and assigned to two groups – dental caries treatment (DCT) and caries-free (CF) – according to their caries experience [decayed, missing, or filled primary teeth (dmft) and decayed, missing or filled secondary teeth (DMFT) values of ≥0]. The CPQ8–10 instrument was administered at baseline and at 4 wk of follow-up (i.e. 4 wk after completion of dental treatment). In the DCT group, increases in CPQ8–10 scores were observed between the baseline and follow-up results. However, longitudinal evaluation of the CF group demonstrated no statistically significant difference in CPQ8–10 scores. Responsiveness of the CPQ8–10 instrument (magnitude of change in CPQ8–10 scores) in the DCT group was greater (effect size >0.7) than in the CF group. The findings of this study show that dental caries treatment has an important impact on OHRQoL of children. The CPQ8–10 was considered an acceptable instrument for longitudinal measurement of changes in OHRQoL.