Is it a good idea to point students to Stack Overflow?
A qualified "maybe."
I can't tell you what the exact ratio of student to seasoned user is because, quite honestly, we don't know that. Students don't generally self-identify. However, I can give you some general observations.
The ratio of neophytes to experts is quite high, and has been increasing over time. The general level of expertise for most new questions nowadays is fairly low. For a time, the site was being overrun with terrible questions, so there are now software mechanisms in place that block at least 25% of newly-asked questions for quality reasons, and account blocks for the worst offenders.
My goal is of course not to delegate my course to SO, but teach student about collaborative work and also how to properly ask a question or report a bug on a forum.
The Help Center article How do I ask a good question goes into some detail about how folks can ask questions productively on Stack Overflow. At the bottom of that article, it links to Eric Raymond's article How to Ask Questions the Smart Way. That's a tough love article, but it describes in detail every possible thing that can go wrong on any Internet support site, including Stack Overflow.
If your students can read those two articles and heed their advice, they'll do fine on Stack Overflow.
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