Dictation can be tough with kid voices (though I do find my daughter's getting a lot better IF she has the patience to practice - and will actually listen to advice about how she needs to to speak if she wants her words recognized -
). We've found word prediction a big help at age 7-8, when voice recognition was too frustrating. And it's easier to use in a classroom full of other people.
In your meeting, it might be helpful to ask them what they would suggest as alternative ways to demonstrate his knowledge - and to what extent and how often they would expect to let him use them.
There are several threads which discuss all sorts of potential dysgraphia accommodations in detail; if you have trouble finding them in a search, I'm sure we can help track them down. Good luck!
