in the school表示在学校；在这所学校

例句：

在学校里每个参与斗殴的人都会受到惩罚，不管是谁挑起的。

Just as the teacher plays the role of leader in the classroom, so does the headteacher play a leadership role in the school.

in class 表示在上课；在上课中

例句：

You can skip the next chapter if you have covered the topic in class.