How much is the baggage allowance for student? Any conditions?

Usually, the free baggage allowance is 20kg for economy class ticket holder. And as of Sep.1, 2011, China southern airlines has increased the baggage allowance to some extent on part of flights routes in Asia, Australia, New Zealand, Middle East, Africa and etc for students. Students could apply for the free baggage allowance increase by showing the related documents when purchasing tickets.