Most studies on the assessment of ICT competences use measures of ICT self-efficacy. These studies are often accused that they suffer from self-reported bias, i.e. students can over- and/or underestimate their ICT competences. As such, taking bias and accuracy of ICT self-efficacy into account, would improve the validity of these studies and the predictive power of the ICT self-efficacy measures used. Consequently, the general aim of this study is twofold. First, to explore the degree to which primary school students are under- and/or overestimating their ability in digital information processing and communication. Second, to identify student characteristics that are possibly related to the accuracy of ICT self-efficacy. Information on accuracy and bias of ICT self-efficacy was gathered by comparing students’ results on an ICT self-efficacy scale and a performance based ICT competence test. Both instruments were administered to 378 sixth grade students from 58 primary schools in Flanders (the Dutch speaking part of Belgium). Information on the explanatory student characteristics was gathered through a questionnaire that was administered to the same students. The results indicate that primary school students make relatively accurate and positively biased judgments about their ability in digital information processing and communication. Further, the results indicate that primary school students’ actual ICT competences and previous ICT experience are related to their accuracy of ICT self-efficacy. As this study is one of the first to investigate primary school students’ accuracy and bias of ICT self-efficacy and to identify potential explanatory variables, it provides new insights into the nature of ICT self-efficacy.