The present study was a longitudinal study. The first step of the research was conducted during 2004-2005 academic year with 190 preservice teachers attending to their first year at Hacettepe University Primary Education department. At this phase, preservice teachers' misconceptions related to relations and functions concepts were identified, classified, and the possible reasons for these misconceptions were investigated. The second step of the research was conducted during 2005-2006 academic year with 97 preservice teachers attending to their first year at the same university's Primary education department. At this phase, the answer of the question "whether the preservice primary teachers' misconceptions related to the functions can be eliminated or not?" was explored. The results showed that the lesson content, lesson plan and the method, which were developed with respect to taking into consideration the general misconceptions identified, preservice teachers' misconceptions were substantially eliminated.