what advice was great when you first heard it, but has aged like milk since then?

Teachers should be using Wikipedia as an opportunity to teach skepticism and following sources. I wouldn't allow Wikipedia to be used as a cited source, but as a starting point for finding other sources on a topic.

Does anyone still say not to trust Wikipedia? They did so in the beginning and it certainly didn’t have to turn out trustworthy so that was good advice for a few years.

Now we see it’s the most trustworthy encyclopedia, and my kids’ teachers qualify it as “an encyclopedia is not an original source “, which is correct and a valuable distinction. They recommend it as a starting point but don’t allow citing it, as is correct.