Less versus Few and Comparative

It's frequent to misuse less and fewer, especially in a comparative sentence. Have a look these two sentences and decide which is wrong:

• In this course there are less students in class
• In this course there are fewer students

When you use plural (countable nouns) the right form is FEW and FEWER and you use LITTLE and LESS for singular (uncountable nouns) or to modify an adjective.

You can go to these links where you can find a really good explanation and some exercises at the end of the page to practise with. Click here or here
If you need further practice, do these exercises:  exercise 1 - exercise 2