In this paper, we study the impact of high-speed internet access on student performance. Our empirical analysis leverages a unique dataset that combines information on ultra-broadband (UBB) diffusion in Italy with data on student performance in 2nd, 5th, and 8th grades for the period 2012–2017. We exploit the staggered roll-out of UBB, starting from 2015. Through an event study approach, we find evidence of endogeneity between student performance and UBB diffusion. We deal with this issue through an instrumental variable approach that exploits plausibly exogenous variation in the diffusion of the essential UBB input. Our results suggest that advanced internet connections significantly decrease student performance in Mathematics and Italian language in the 8th grade. In contrast, we do not find any significant effect in the 2nd and 5th grades. Male students from low-educated parental backgrounds are those more adversely affected, especially if they attend schools with a low IT usage. •We study the impact of high-speed internet access on student performance.•We use a unique dataset that combines information on ultra-broadband (UBB) diffusion in Italy with data on student performance in 2nd, 5th, and 8th grades.•We deal with the endogeneity of UBB roll-out through an instrumental variable approach that exploits the diffusion of the essential UBB input.•Our results suggest that advanced internet connections significantly decrease student performance in Mathematics and Italian language in the 8th grade.•Male students from low-educated parental backgrounds are those more adversely affected, especially if they attend schools with a low IT usage.