原句：The students have lessons at school.（学生们在学校上课。）
否定句：The students don't have lessons at school.（学生们不在学校上课。）
肯定句改否定句的方法：
1、be动词后加not，诸如：is not(isn't)， are not(aren't)， was not(wasn't)， were not(weren't)， am not（无缩写）。
◆ He is a student. 他是一个学生。--- He is not a student. 他不是一个学生。
◆ They were watching TV then. 那时他们正在看电视。--- They weren't watching TV then. 那时他们没在看电视。
2、情态动词等后加not，诸如：can not(can't)， will not(won't)，should not(shouldn't)，must not(mustn't)，need(needn't)等。
◆ She can take care of herself. 她能照顾好她自己。--- She can not(can't) take care of herself. 她不能照顾好她自己。
◆ You should go home. 你应该回家。--- You shouldn't go home. 你不应该回家。
3、若无法找到be动词或情态动词，就在已有动词前额外加助动词否定形式：don't/doesn't/didn't，同时将动词变原形。
◆ She likes the room. 她喜欢这房间。--- She doesn't like the room. 她不喜欢这房间。
◆ We did our homework yesterday. 我们昨天做了作业。--- We didn't do our homework yesterday. 我们昨天没有做作业。
注：句中若有some ，须将其改成any。
◆ I want some books. 我想要一些书。--- I don't want any books. 我不想要任何书。
◆ There is some water in the cup. 杯子里有一些水。--- There isn't any water in the cup. 杯子里没有水了。
The students have not /haven't /have no lessons at school.
The students don't have lessons at school.