As a student doing research for homework, how would I know which to trust?
What you want is a research journal, such as the Journal Of the American Medical Association, the Journal Nature or some other academic or research journal. These are sepperate from other publications and if you go to a university or even a high school, you can ask the librarian if your school subscribes to any or has a database of them which can be accessed.
Some journals may carry a couple of editorials or general news items in the front, but generally peer-reviewed studies and reports are easy to find.
The peer review process is less than perfect, but it's pretty good. Obviously it is impossible to validate all studies, without completely auditing them and even redoing the studies to make sure they are correct, but the peer review process is about the best you could reasonably expect and usually works very well.