DS7 is all over the board as far as grade levels go. When people actually need to know, I say he's working at about a 5th grade level because that's about the average level of his work. But, we have ranges from grade level (handwriting) up through high school (reading).
With fellow homeschoolers we say "well, it depends on the subject" and then laugh and give his age. Usually that's not a problem with homeschoolers, most just ask the kids ages (I also have 2 younger ones who aren't doing formal school yet).
For people like the cashier at the grocery store, we answer, "Well, we're homeschoolers, but he would be in x grade if he were in school."
