Students of Czech as a foreign language quite often encounter a problem with the distinction of prefixes s- and z- in writing. In some cases, it may significantly change the meaning (cf. směna x změna).
Not only Czech textbooks for foreigners pay attention to this topic but also grammars and spelling manuals, as native speakers often face the same problem. This paper looks at the mentioned issue from the point of view of a foreign student and a teacher of Czech for foreigners, for whom corpus data represent a new way of approaching the problem with prefixes.
The aim of this work is to present a corpus-based approach to the problematical issue and also to suggest a way to practice it in a form of corpus-based exercises. Attention is also paid to the possibilities of automatic extraction of word pairs from the corpus with the prefixes s- and z- using the Morfio tool.