Foreign Language Teacher Education programmes (FLTE) are designed to train teacher candidates to teach at elementary, secondary, and tertiary levels. The case necessitates prospective teachers of English (PTEs) to be equipped to teach all these levels/age groups distinctively. Having a course specifically designed for young learners (YLs), but lacking one focusing on teenagers/young adults, the study intended to draw attention to the need for improvement in the FLTE programme components with the development and implementation of a remedial course design. With this purpose, the study analysed the needs of prospective teachers, investigated possible solutions and presented a course design as a practical suggestion. This qualitative study was conducted with 10 senior ELT students at a state university in 2019-2020, utilising focus-group interviews and two metaphor-based prompts. Based on the preliminary findings, a remedial course was designed with a practicum supplement. Following the implementation of the course design, the effectiveness of the intervention was investigated. Overall findings revealed that the present FLTE program did not sufficiently prepare prospective teachers for teaching teens/young adults, and there was an immediate need of equipping them for teaching teens/young adults and implicated that the programme courses should target at all levels by considering the theory-practice balance and that practicum opportunities be expanded and improved. Moreover, the suggested course was found to contribute to the PTEs' sense of preparedness, awareness and acceptance of target learner characteristics, knowledge of appropriate instructional strategies and techniques, and led to a change in the PTEs' attitudes towards teaching teens/young adults.