The science teacher in the modern high school acts as the designer and driver of the in-class practice. In this role, the teacher must broadly assess the effect of the practice on the student. This would rely on accurate self-knowledge of how they act in class and impact their students. In this study we explore these issues by comparing the difference in responses of 86 teachers and 2512 Year 9 and 10 students to an instrument probing their perceptions of their in-class practice. We report two significant findings. First, not only do teachers constantly positively overrate their in-class practice but secondly, these perceptions are completely unrelated to how their students see their classrooms. This implies that using teachers as the sole source of evaluation about their own classroom practice is problematic and that evaluation should always be endeavoured to be undertaken at the level of both teachers and students.