Bullying is a problem that affects children and teenagers around the world and its repercussions can endure throughout adult life. The main objective of this research is to study the incidence of bullying on the academic performance of students in schools in the Madrid Region. The databases used are those of Competency Tests, a census evaluation carried out on all 10th grade students in Madrid during the year 2017 (almost 32.000 students). To analyze these data, we carry out a multilevel methodological approach to identify the quantitative association of bullying with academic performance and to estimate the probability that performance is affected by the level of bullying that exists in the school. The results indicate that bullying has a negative correlation with all the competencies evaluated and that bullying can affect students with low or high academic achievement in different ways, depending on what competency is evaluated.