This study aims to investigate the nature of different mathematics teaching modes (prescriptions) that guide prospective teachers during their instruction. The participants were 24 junior prospective middle school mathematics teachers (19 females and 5 males) who were attending a mathematics methods course at a private university in central Turkey. Each participant was tasked with applying an innovative prescribed curriculum about equivalent fractions to a single elementary or middle school student; he/she is required to videotape the teaching session. We collected these teaching videos and analyzed them through a phenomenographic approach. Results suggest that the participants select and operate with certain teaching prescriptions while teaching. The mathematical knowledge of the teacher is not the only factor that affects his/her teaching; ingrained prescriptions influence and guide their teaching as well. All these teaching prescriptions are selected according to the teachers' strongly held beliefs about teaching and learning based on their prior schooling experiences and not on their experiences in their coursework. We also found that having prospective teachers operate with an innovative curriculum does not improve their teaching in the presence of these prescriptions.