This mixed-methods study investigated perceptions and knowledge about content and language integrated learning (CLIL) and bilingual education. Data were collected using surveys, questionnaires and semi-structured interviews from 26 content-based teachers in Valledupar, Colombia, before and after their participation in an online training program. Findings revealed that teamwork and administrative support are crucial factors for a successful CLIL implementation. However, results also showed that teachers knew very little about the CLIL approach, although they claimed to have been using it at their schools for 3-4 years before the study, suggesting that any previous in-service teacher training had not resulted in an adequate understanding of CLIL or bilingual education for the context.The teachers’ perceptions of CLIL and bilingualism were more positive after the training, and they reported understanding similarities and differences between both concepts. Hence, there is a need for more specialized training (material design, planning, communication, and assessment) to better prepare in-service teachers for bi-/multilingual learning environments, which in turn would provide teachers with much-needed tools for more effective delivery of CLIL-oriented solutions.