成绩不好用英语这样说：The result is not good
result 英 [rɪˈzʌlt] 美 [rɪˈzʌlt] n.结果;（尤指足球比赛的）胜利;[体]比分;成功实现的事
vi.发生，产生;归结为，导致;后果，终结;由…而造成[产生]
good 英 [gʊd] 美 [ɡʊd] adj.好的;优秀的;有益的;漂亮的，健全的 n.好处，利益
比较级 better 最高级 best
not 英 [nɒt] 美 [nɑ:t] 不;[用以表示否定、否认、拒绝、禁止等]不是;
例句如下
You use not to represent the negative of a word, group, or clause that has just been used.
译文：用于表示对刚提及的单词、词组或从句的否定。
Not all the money, to put it mildly, has been used wisely...
译文：说的好听些不是所有的钱都花对了地方。
The houses are beautiful, but there's no shop, not even a pub to go into.....
译文：这些房子很漂亮，但是周围没有商店......
有关good例句
We had a really good time together.
译文：我们在一起度过了美好时光。
Exercise is just as important to health as good food.....
译文：锻炼和合理膳食同等重要。
On balance biotechnology should be good news for developing countries...
译文：总的来说，生物技术对发展中国家应该是有利的。
关于result的例句
Compensation is available for people who have developed asthma as a direct result of their work.
译文：直接因工作原因患上哮喘的人会获得赔偿。
Fifty per cent of road accidents result in head injuries.....
译文：50％的道路交通事故都会导致头部损伤。
What was the result?' —One-nil to Leeds.
译文：“比赛结果怎样？”——“利兹队以1比0获胜。”
参考资料
耿小辉.《零基础英语语法》.上海：中译出版社，2017