这个问题我会，虽然本人英语口语不是很好，但是对英语四六级词汇还是很熟悉的~下面给大家从三个方面具体解释一下：
一、含义不同
on class指在种类上。
in class指在课堂上；上课中。
二、用法不同
in class，指地点比较合适。someone is in class。相当于someone is in classroom.
on class，指时间比较合适。someone is on class.相当于someone is busy, not free, is on class.
三、例句：
Does the quality of teaching depend on class size?
教学质量取决于每个班的人数吗？
He has already caused apoplexy with his books on class and on war.
他关于阶级和战争的`书已经激起了极大的愤怒。
She keeps good discipline in class.
她严格执行课堂纪律。
She was admonished for chewing gum in class.
她在课堂上嚼口香糖，受到了告诫。