The purpose of the study was twofold. First, it investigated the kinds of writing tasks in textbooks used by senior high school students in Japan. Second, it examined the Common European Framework of Reference for Languages (CEFR) levels of the writing tasks in English-language textbooks for Japanese senior high school students. The study focused on the authorized "English Expression I" Japanese textbooks. The series of seven "English Expression I" textbooks contains 100 writing tasks, which were analysed to see how their types matched the CEFR criteria. Rasch modelling was then used to assess the difficulty of six selected writing tasks. A total of 158 Japanese senior high school students participated in the main research. They were asked to write six English compositions without using a dictionary and were given twenty minutes to write each composition. The research was conducted over a period of one week. The results of the modelling suggest that writing a self-introduction is more difficult than other writing tasks, such as writing about interests and daily life. More than half of the writing tasks in the textbooks were categorized as writing about "oneself" rather than writing about "others", and most tasks belonged to the CEFR A1 level.