This article deals with the use of Open Source Software (OSS) at the primary and secondary level of education in Slovenia. The challenges and advantages of using OSS in educational processes are discussed. The main advantages of OSS are: economic freedom, stability, reliability and a possibility of making modifications but - on the other hand - the main problem for schools can be installation and support. The research carried out to determine the use of OSS in schools is described and the results are compared with the results of similar research studies in Germany, Sweden and UK. The results of both surveys show, that Linux and OpenOffice.org are the most popular OSS applications on computer desktops. The most important conclusion (according to our research) is that lack of knowledge prevents a faster introduction of OSS in education.