Do you think there needs to be a comma in this sentence or is the 2nd one correct?

Question

1a. Students, who study hard, should do well on the test.

2a. Students who study hard should do well on the test.

Or the more I read it the more the first one sounds better!

Answer 1

No, 2a is the correct answer. If you say 1a, you assume all students study hard.

This is rarely the case

Answer 2

OK, I can understand that, but it sure doesn't look right. I really appreciate your help tonight.
THANK YOU VERY MUCH!!!

Answer 3

DrWLS is correct -- it's 2a.

http://grammar.ccc.commnet.edu/grammar/commas.htm
Read #4.