The goal of the research was to assess the level of Digital Literacy (DL) among teachers. The study was diagnostic in order to show DL in six selected key areas: the ergonomics of using ICT, assessing the credibility of information, secure online communication, maintaining anonymity in the digital world, safe logging-in, and intellectual property. DL was measured using a knowledge and competence test. The study was conducted in Poland in 2017/2018 among 701 primary school teachers (primary being the second stage of education). Based on the data collected, we have noticed the following: DL is a heterogeneous concept; the respondents possess the lowest level of knowledge in the area of intellectual property law and know the most about ergonomics; gender does not determine the level of knowledge and competencies in the group. Furthermore, the Dunning-Kruger effect is noticeable among the teachers, in the context of evaluation of DL related to digital safety. We also need to emphasise that for teachers, DL is one of the key protective factors in digital safety, viewed holistically, in schools. Thus, diagnosing and facilitating the development of DL has become one of the key challenges faced by schools today.