Teachers’ inclusive attitudes are one of the most important factors to promote a fully inclusive society. In turns, they are shown to be influenced by various factors such as teachers’ self-efficacy or students’ type of learning difficulty. Inclusive education training has also an impact on teachers’ inclusive attitudes and behaviors. However, while the literature consistently shows such a positive effect, there is little evidence on the optimal duration and content to consider when designing such trainings. To address this question, we conducted (1) a systematic review of literature to examine the effects of content and duration of the trainings and (2) a set of semi-directive interviews among general teachers of the French northern region (both studies are pre-registered). The systematic review on 36 interventions showed the overall positive effect of both stand-alone and infused trainings as well as information based cognitive and mixed ones. Moreover, twenty-four semi directive interviews by using a thematic discourse analysis revealed that supplemental needs such as a need of interprofessional collaboration with other social and medical professionals (e.g., special educators, speech therapists, etc.) should be emphasized in an educational teacher training. Such findings allow to inform educational policy makers when it comes to conceive a successful training to be further implemented in the university curricula to promote a fully inclusive school setting.