When educators say that Wikipedia is not reliable, what they usually mean is that serious work should be based on primary sources, not secondary sources like Wikipedia or any other encyclopedia.
Wikipedia is good for casual research, and in practice, I found the English Wikipedia very reliable, at least for scientific topics, but it is also pretty good on big controversial subjects. Reliability only starts to drop on minor subjects.
But educators want you to go beyond that. Here, Wikipedia is just a starting point, with its best feature being citations.