I'm assuming you can pair the data before and after by student?  That is, you know for Student A this was the before score, and this was the after score?

In that case, you want to use a paired test like paired t-test or two-sample paired rank-sum test.

Be sure to read all the assumptions of these tests before you use them.

If you use something like the rank-sum test, be sure you understand the interpretation.  People sometimes say it is a test of medians, but that isn't necessarily true.

You can read what I wrote about these tests:

Paired t-test:

http://rcompanion.org/handbook/I_04.html

Paired rank sum test:

http://rcompanion.org/handbook/F_06.html

Thank you for your reply and the links, both have helped me greatly and solved my doubts.

as your data is very small, so you can not apply the parametric tests i.e. t test. In this case you can apply non parametric test like Mann-Whitney U test