This article presents the current development of e-learning in Slovenia, with an emphasis on the domestic E-um web portal (URL: www.e-um.si) for teaching mathematics in primary and secondary schools. Based on findings from recent scientific research, the strengths and weaknesses of e-learning materials in education, particularly in mathematics classes, are analyzed. We are particularly interested in the advantages and disadvantages of interactive e-learning materials in comparison to traditional learning materials as well as in the quality of the E-um web portal in comparison to similar educational web portals at home and abroad. Theoretical findings are tightly interwoven with examples of teaching practice using the E-um interactive materials.