It is important to recognize that wikipedia isn't subjected to a rigorous review process like anything published is, but it's not necessarily wrong. Most of what's on wikipedia is completely valid information.
I use the math and science pages for school (college, senior, physics) and my job (weather forecasting/analysis) all the time. And I have never used something that turned out to be totally wrong. I have only noticed a few incorrect facts over the years, and I have corrected them.
Of course you can't cite wikipedia in a paper, or use formulas from it without verifying them and the results you got. But sometimes it will provide insight that can't be found anywhere else without doing a lot more searching.
Any school that blocks wikipedia needs new administrators.