Christine, I'm about as liberal as you can get in regard to
respecting students' own language (see the NCTE statement on
student's language). If chatting with a student in my office,
I would never correct her, even if her dialect tossed up
something so removed from SE as "had went." If you start stopping
a person in mid-sentence to correct their grammar, they're
going to stop talking to you--and rightfully so! Suppose for
example, you started criticizing me for using "singular THEY"
on e-mail posts--I'd stop responding to your queries!
 
On drafts of essays written for college courses I teach, I put a squiggly
line under incomprehensible, awkward, or ungrammatical (relative
to SE) phrasing, which means: "Rephrase." If I found that a
student didn't know how to change "had went" to "had gone,"
I would show her.
 
        --Bill Murdick