Inclusive education is fundamental, consisting of enabling all students, irrespective of their characteristics, to receive appropriate education and actively participate in school life. Teachers play an important role in this regard; thus, this study aims to analyze teachers’ perceptions regarding their preparation for inclusion by assessing possible differences depending on the educational stage (early childhood, primary, or secondary education). A total of 1098 Spanish teachers, from Extremadura, responded to three dichotomic answers about their inclusive education preparation perception and the Evaluation of Teachers’ Inclusion Readiness (CEFI-R) questionnaire, a 19-item tool composed of four dimensions: (1) conception of diversity, (2) methodology, (3) support, and (4) community participation. Pearson’s chi-square test was used to assess differences between the dichotomous questions and educational stage; Kruskal–Wallis was used to determine whether the educational stage conditioned the CEFI-R dimensions responses, and the Spearman rho was used to test the association between age groups and the CEFI-R dimensions. Statistical differences were found between secondary education and preschool education and primary education teachers in the dimensions (1) conception of diversity, (2) methodology, and (3) support. Significant differences in dimension (4) community participation between preschool education teachers and secondary and primary education teachers were found.