Wikipedia: follow your teacher's guidelines
I think Wikipedia is really useful, but many teachers have the opposite point of view. They are concerned that anyone could edit a page and put in falsehoods, and are concerned that it does not seem to be "official". The most obvious piece of advice therefore is to always follow your teacher's instruction about the use of Wikipedia.
Wikipedia is not a peer-reviewed academic journal
Actually Wikipedia is in fact peer reviewed, but if you are in Year Twelve doing an extension course and you are expected to be finding resources that are from academic journals, do not use Wikipedia.
Even if your teacher bans it...
Even if your teacher bans Wikipedia, scroll to the end of any Wikipedia article and there you will find a wonderful array of resources that have been used in writing the article. Many of these will be online, and some of these may be exactly the resources you have been looking for. Use Wikipedia for the links even if your teacher does not want to see it in your bibliography.
Wikipedia or Encyclopedia?
Modern Encyclopedia's are all online, but even modern online encyclopedia's cannot keep up with Wikipedia. Wikipedia will often have...
- articles about breaking news and events that have only just happened
- articles written by leading scholars in the field (thus often greater diversity of excellent sources than an Encyclopedia)
- significantly greater detail in articles than any Encyclopedias
But is biased and people post prank articles...
Everything is biased, but not everything publishes ALL corrections, suggestions for corrections, sources and discussions about accuracy. Click over to the History tab of a Wikipedia article to see everything that has gone on behind the scenes.
Prank articles are posted...and then they are found, corrected and removed or edited.
Where there are major disagreements about how to present information (or the accuracy of information) the main article is flagged with special notes to warn you that, for instance, more accurate sources are still needed.
To sum up
If your teacher does not ban the use of Wikipedia you should use it comfortably for school research provided that you remember to triangulate (look at more than one source). If you are working at University level (i.e. doing HSC Extension work) you may need to avoid sources like Wikipedia if you are supposed to be ONLY using peer reviewed journal articles. If your teacher does ban Wikipedia, then certainly still use the references at the end.