Teachers’ attitudes toward inclusive education appear to be an important factor to promote a fully inclusive society. Research shows that they are strongly influenced by teacher, student and environment-related factors. Teachers’ training on inclusive education is one of them. However, while the literature is concordant to show this effect, there is little evidence on the optimal duration and content to include in such programs when it comes to conceive them. Our systematic review (preregistered on https://osf.io/4fmsu/) investigated the impact of the education inclusive trainings on teachers’ inclusive attitudes, and examined the effects of the content and duration of such trainings on this variable. Thus, 36 preservice teachers’ training programs were examined. Overall, the majority of programs (69.4%) induced the positive change in attitudes toward inclusive education, confirming the robust impact of the teacher training programs in attitudinal shift. As for the content and duration, both mixed and theoretical, as well as short- and long-term programs seemed to be efficient in inducing the positive attitudinal change. These descriptive findings were also confirmed by the supplementary chi square tests and multinomial logistic regression that yielded non-significant effects of content and duration variables on the obtained efficacy of the program. The implications as well as open science issues in this domain of research are discussed.