This case study examined the characteristics of classroom discourse during physics lessons in two single-sex high school classes–a boys’ vs. a girls’ class. All lessons were taught by the same teacher and covered the same topics. For each class, six lessons were recorded, transcribed, and coded and the characteristics of the discussion were counted, including the number of words spoken by the teacher and students, the number of open-ended and closed-ended questions posed, and the number of open and closed discourse segments and their initiator. A total of 549 closed-ended questions, 1,151 open-ended questions, 139 closed and 168 open discourse segments were analyzed. A semi-structured interview was conducted with the teacher on his views of the discussion characteristic in his lessons and the differences he has observed between boys and girls in terms of these characteristics. The average number of all classroom discourse parameters examined was similar in both classes and no significant differences were observed. In both classes, the students participated very actively in the discourse throughout most of the lesson, both among themselves and with the teacher. From the teacher’s perspective, the differences in discussions between the classes, if any, are not related to the student’s gender, but rather to the character of the students and the classroom environment. The main conclusion that emerges from this study is that the girls’ discourse in a single-sex class does not differ significantly from the boys’ discourse, as discussed in the article.