The difference between these two is that the first is he didn't want to go to school and the second is he just didn't go to school but maybe there are some other reasons rather than he didn't want to.

第二个才是对的。过去时里要用 “ 没 ” 或 “ 没有 ”，如：今天早上我没（有）吃早饭。 他们没（ 有 ）告诉我这件事。 这个句子如果要用 “不 ” 的话，你要改成：明天我不去学校。（将来时） 如果用将来时的话，则不能说：明天我没去学校。一定要说：明天我不去学校。

他“不”来，means he will not come 他“没”来，means he didnt come

昨天他不去学校：He didn't want to go to school yesterday.(it is a reason) 昨天他没去学校：He didn't go to school yesterday.(it is a result)

To tell the difference, compare these two: 他不去学校。(He is not going to the school. / He doesn't go to the school.) 他没去学校。(He didn't go to the school.) In the first sentence, the main focus is ---- the action of not going was "made" by "他." In the second sentence, the main focus is --- he was "not present" or "did not make it" to the school. IMPORTANT: When using 没 + verb , this indicate an past event. E.g. 没吃 didn't eat, 没喝 didn't drink...etc. Therefore, you can only use 没 for past tense. Now, put the time phrase 昨天 back into the sentence. 昨天他不去学校。He wasn't going to the school yesterday. 昨天他没去学校。He didn't go to the school yesterday.