Usually teenagers and adults have studied English before at school or high school and probably have their own manner of learning. For instance, an adult can learn in better way with lots of grammar and then when he is learning the language through communicative activities, speaking or writing, he may feel uncomfortable or feel that he is not learning at all. The learners may accept new changes in method however, they may want to learn in the same way than before.
Biography:
Spratt M., Pulverness A., & Willians M. (2015) The TKT Course Modules 1,2 and 3. Cambridge English. Second Edition.