This may be a good general idea for life, but definitely not for school. Kids in school can be downright turds. Some of those kids would literally laugh at people in wheelchair or crutches. And when you call them out on making fun of your stuttering, somehow more people will join them in laughing at you than sympathize with you. The world isn't a rational place. I know all schools aren't like that and that maybe in some schools the kids are nicer, but that's the harsh reality. If you're not the aggressive type, just walk away. Nothing makes a bully rage more than their need for attention being dismissed like dirt. Don't look at them, don't shake your head, don't say anything. Just walk away as if they were not there.