Effective removal of dental plaque is essential factor for prevention of caries, gingival, and periodontal diseases in children and adults. To evaluate factors associated with improving toothbrushing performance (TB-P) among children. An observational cohort study analyzed all paediatric patients receiving regular examinations in a single dental clinic between 2009 and 2017 and regularly brushing their teeth with a triple-headed toothbrush (TH-TB). At every periodic follow-up, the TB-P of the child/parent was evaluated using the TB-P Skill Index (TB-PS-I); that is, did the child reach all five teeth segments within each arch and did he/she perform 10 back-and-forth stocks in each segment. When not optimal, they received instructions for improving TB-P and subsequently were asked to re-demonstrate. TB-PS-I was calculated and analyzed for correlation with other explanatory variables. A total of 1737 children with 7399 follow-up appointments were analyzed. Older age, female gender, higher number of follow-up appointments, and compliance with twice-daily toothbrushing significantly improved TB-P. The most typical mistakes in their performance were not reaching the canine segments and not performing enough strokes in each segment. Instructions given after imperfect TB-P significantly improved the TB-P. The magnitude of improvement, however, did not correlate with the performers' age, gender, or the number of follow-up visits. A significant percentage of children >8 years did not perform optimal toothbrushing even when using TH-TB.