The aim of this research is to examine developments of primary school teacher candidates' mathematics teaching performance according to peer assessment. Primary school teacher candidates practiced teaching skills within the scope of the Teaching Practice. This research is a longitudinal study. The research's study group has fifty-eight primary school teacher candidates. According to the results of the research, peers rated primary school teacher candidates' final mathematics teaching performance higher than their first mathematics teaching performance. According to the peer assessment, primary school teacher candidates' mathematics teaching performance has improved over time. Accordingly, a significant difference was found in the first (preparation for lesson and lesson association) and second (teaching process) sub-dimensions of the scale when first mathematics teaching performance scores controlled. The source of the difference between peer assessment scores regarding first and second sub-dimensions of the scale can be said the number of teaching practices in mathematics. The primary school teacher candidates who practiced 2 times in mathematics got lower scores in the first and second sub-dimensions than those who practiced 3 and 4 times. According the result, primary school teacher candidates should practice at least 3 times in order to ensure their development "preparation for lesson and lesson association" and "teaching process" for mathematics teaching performance.