We present an overview of how teacher training can work as a key element in good professional performance with students at risk of exclusion. The work derives from a doctoral thesis that analyzes a school reengagement program in the region of Murcia (Spain): Occupational Classrooms. The research was theoretically based on an ecological approach of risk of educational exclusion and a multidimensional approach of school engagement. Focusing on a mixed-methods approach with a multilevel convergent nested design, it was possible to investigate multiple levels: macro (policies), meso (school), and micro (classroom), as well as interrelated elements that influence in the possibilities of re-engagement of these students. The results showed notable deficiencies in the professional performance of teachers working with students at risk, revealing difficulties in the professional development of teachers linked to administrative, institutional, cultural, and personal determinants. Similarly, negative repercussions were detected stemming from the involvement of the teaching staff and on the results of the students and their options for continuity in their educational trajectory. To conclude, the importance of cultivating both the necessary conditions for adequate training, as well as those aimed at making teachers feel supported, included, and recognized, were highlighted in this study.