Monitoring bullying behaviours is the key aspect of a successful anti-bullying intervention. Questionnaires among pupils and principals of the same schools were utilised to measure the agreement between pupil-reported frequency and principals' estimations of the prevalence of frequent bullying in the same schools and to identify monitoring methods associated with the best agreement. The correlation between the pupil-reported frequency and the principal's estimate of the prevalence was weak. Two-thirds of the principals estimated the prevalence of frequent bullying in their schools to be four percentage points lower than the prevalence, based on pupils' reports. Questionnaires that were developed and administered by the schools themselves and unspecified monitoring methods were associated with the best agreement between pupils' reports and principals' estimates of the prevalence of frequent bullying. There is a clear need to communicate better the nationally collected data back to schools. It seems that despite the monitoring efforts, school principals were not aware of the prevalence of frequent bullying as perceived by their pupils. Awareness of the problem may require more than just available evidence.