This study analyses the practicum – the initial teacher training practice period- and its impact on a group ofsecondary education student-teachers in the Balearic Islands (Spain). The study uses a qualitative case researchapproach to understand the construction of teacher identity during the practicum period. Six cases from differentteaching specialties were examined. The findings showed that learning experiences such as observing otherteachers contributed to the construction of teacher identity in the student-teachers, either by identification with ateaching model, or by opposition to a teaching model. In addition, having the opportunity to teach to differentgroups of students helped them develop the feeling of being a teacher. Feeling part of the community of teachersand interacting with other teachers also led to teacher identity development. Moreover, the results indicated thatthe feedback they received also contributed to teacher identity construction. The study also revealed some badmentoring practices. Even though these findings contribute to the studies regarding teacher training education andmentoring practices, the results of this study correspond to the perceptions of six participants, so further researchon this field would be important for a wider understanding of teacher identity construction in student-teachers.