This case study was conducted to explore the development of pedagogical content knowledge (PCK) through a school practicum course. The case study also examined how observation of number pattern lessons in schools and discussions of these observation contribute to prospective teachers’ PCK. The participants of the study were three female prospective elementary mathematics teachers, who enrolled in a 4-year teacher training programme in a university in I˙zmir, Turkey. With regard to the issue of effectiveness of the activities in the SP course, it can be concluded that observations in real classroom settings and discussions of these observations in the SP course resulted in an improvement of the prospective teachers’ PCK.