I think that sixth-graders could differentiate between an "Appeal to ignorance" and a "Straw Man":
My opponent is trying to convince you that we evolved from monkeys who were swinging from trees; a truly ludicrous claim.
"Look! It's a strange beam of light moving through the sky. I don't know what it is, so it must be aliens visiting us from another planet. "(These examples are pretty lame . . . I know. Put better ones in the comments if you're reading this.)
Educators consider residue - "learning that lasts" - in determining curricula and teaching methods. How will a student be affected by a course fifteen years after taking it? Exposure to logical fallacies will get students identifying arguments and thinking critically about them even if they aren't strong readers. And, fifteen years out, I'd wager that the average student would be much more likely to recognize a "straw man" than a "dangling participle."
