This case study discusses the integration of differentiated instruction into a TESOL Methods course in a language teacher education program in northwest Taiwan. Forty-six undergraduate students’ lesson plan designs and teaching practices in elementary schools were analyzed. Participants constructed knowledge and skills about differentiated instruction through four stages, from having no idea about differentiated instruction to being able to implement tiered worksheets in elementary school English classes. Results indicate that the importance and knowledge base of differentiated instruction as well as the instructor’s real demonstration of differentiated instruction among elementary school students should be included in language teacher education programs.