Hello Woojung,

Thank you for submitting your homework.. Please take notes of my corrections.. See you  in our class..^_^

Corrections:

 I think punishment is a good for students that behave badly because it will help them think they did a wrongthing.

Correct: I think punishment is good for students who behave badly because it will help them realize that they did a wrong thing.

**Do not use a determiner (a, an, or the) for an adjective. The relative pronoun 'who' is better to use than 'that' in this case. Although 'that' can be used on nouns, too; it is only used when the idea introduced is important. Instead of 'think', you can also use the word realize, which means "to notice or understand something that you did not notice or understand before".

 I also think the punishment is not always good thing because student can think its nothing and keep behaving badly.

Correct: I also think that punishment is not always good because the students may think that it's not a big deal and may keep behaving badly.

** Use the conjunction 'that' to introduce your thought. There may also be no need for a determiner before the word 'punishment'. You can either say 'not always good' or 'not always a good thing'. The first one is only with an adjective so there is no need to use a determiner, while the second one has the determiner 'a' to refer to the noun 'thing'. 'May' is a modal which states possibility.