Motivation has been studied throughout the field of language acquisition for the past 20 years. Demotivation has also been researched in Japan at primarily the university and high school level. To provide a deeper understanding of demotivation for Japanese junior and senior high school learners, this study explores the following three questions. (1) What are the differences between demotivators for junior high school learners and high school learners in Japan? (2) Which factors are ranked higher or lower as demotivators for junior high school learners and high school learners in Japan respectively? (3) How do the strong demotivators change over time in high school? The participants for the study were 234 first year Japanese students from two public high schools in northern Japan, and 217 freshmen from two universities in the Kanto region of Japan. 8 Students were interviewed. A 44-item questionnaire with 1-5 Likert Scale was used to explore demotivation for the learners. The results show that Nature of English is more demotivating for junior high school learners; Lesson style and Teachers are more demotivating for high school learners. Among junior high school learners, Tests, Nature of English, and Reduced self-confidence are more demotivating than other factors. Among high school learners, Reduced self-confidence, Lesson style, and Textbooks are more demotivating than other factors. (Contains 9 tables and 2 figures.)