This study aims at documenting the challenges that three Mexican students participating in a Content-Based Instruction (CBI) module from a Master's (MA) program in English Language Teaching (ELT) face when writing content and language objectives for CBI lessons. Through qualitative research based on a content analysis design, one lesson plan of each MA student (n=3) was analyzed using criteria proposed by well-known researchers. Results revealed that MA students wrote clear content objectives. The major challenge of content objectives was found in the observability of these objectives. "Language" objectives were less successful, as most of them were rated as "not clear." Moreover, language objectives focused almost exclusively on language skills and grammar and language structures. Finally, the verbs used in the language objectives demanded a low-order cognitive category from students. Despite being EFL trained teachers, these MA students had more challenges in writing language objectives than content objectives. Thus, material, examples, and directions provided to students should explicitly draw students' attention to the most common challenges to help overcome them.