Digital literacy should be a part of every subject:
http://plpnetwork.com/2014/03/26/infuse-digital-literacy-curriculum/
The article links to a useful checklist for students to evaluate their sources using the CRAAP checklist:
http://www.ufv.ca/library/how-tos/evaluating-information-the-craap-test/
(Or here, in more of a handout-type format):
http://nbarker.wikispaces.com/file/view/CRAAP+Test+handout.pdf
CRAAP stands for:
Currency
Relevance
Authority
Accuracy
Purpose