The current study investigated whether children's conformity to a majority testimony influenced their willingness to revise their own erroneous counting knowledge. The content of the testimonies focused on conventional rules of counting, by means of pseudoerrors (i.e., unconventional counts) occurring during a detection task. In this work measurements were taken at two different time points. At time 1 children aged 5 to 7 years (N = 88) first made independent judgments on the correctness of unconventional counting procedures presented by means of a computerized detection task. Subsequently, they watched a video in which four teachers (unanimous majority) or three (non-unanimous majority) made correct claims about the counts and children had to decide whether the informants were right or not, and justify their answers. Our participants conformed significantly more when the correct testimony was provided by a unanimous majority than by a non-unanimous majority. In addition, in two of the three pseudoerrors presented, there was no difference in the children's tendency to conform to unconventional counts as age increased. At time 2, which was taken to test whether the effect of the testimony was maintained over time, the responses of the 32 children (16 from each age group) who had endorsed the claims of the unanimous majority at time 1 revealed that teachers' testimonies only had a lasting influence on elementary school children's understanding of conventional counting rules.