The paper analyses possible reasons for the gap between teachers' actions and intentions, reported by research on practices with the use of ICT. The theoretical approach is informed by teachers' beliefs, which are discriminated in two categories: pedagogical and epistemic. A qualitative fieldwork research undertaken in eight public primary schools in Rio de Janeiro between 2014 and 2019 presents empirical evidence of the relationship between ICT use in the classroom and teachers' beliefs. Data collection took place in two phases, and the data set consists of: (1) sixty four semi-structured interviews with teachers of the eight schools; (2) two focus groups with teachers in two schools, selected among the eight initial schools. Main findings show the importance of ICT self-efficacy at the core of teacher's pedagogical beliefs, as skills and knowledge are built upon direct experience and observation of others. Furthermore, epistemic beliefs are strongly related to pedagogical beliefs and teachers' attitudes. Findings show that the most innovative teachers are those who conceive ICT as a cultural artefact, have an ecological view of the classroom, and translate their intentions into actions, facing uncertainty and possible failure.