In spite of the multiple competencies necessary to design and deliver proper Content and Language Integrated Learning (CLIL) lessons, the teachers' linguistic proficiency is the primary competence considered in the accreditation of CLIL teachers in Spain. However, teachers' competence in planning CLIL lessons is key to bilingual education. This article explores this competence and reports on the several factors that influence the level of integration of CLIL methodological principles in the lesson planning style of in-service teachers at primary and secondary education. The factors studied are the stage of education, curricular subjects, teacher education, status at school, years teaching CLIL and type of school in a sample of 383 in-service CLIL teachers. Results show statistically significant differences in all the factors studied except in the stage of education (primary-secondary) and the type of school (state-semiprivate). These results reveal a high heterogeneity in the sample, which allows the description of the CLIL teacher profiles according to the factors that influence their competence in planning and delivering CLIL lessons. It is concluded that education and training in CLIL competencies, such as planning CLIL lessons, is also necessary in order to achieve a more homogeneous competence profile of the teachers. Therefore, a review of the academic programs and of the accreditation model so as to guarantee that they include prescriptive education and training in CLIL is recommended, since the quality and sustainability of bilingual programs also depends on teachers' competence in CLIL and not only on the students' academic results.