K has a peanut allergy, and I used to share a dishwasher with my mom who despite all my complaining used to put peanut butter things only barely rinsed in all the time. He survived. Dishwashers as a rule do seem to do a good enough job that they don't let anything important to the allergy stick around. If your dishwasher is good you shouldn't have to worry. I would be more careful about things like wooden spoons and stuff like that that might have absorbed oils but don't get washed in the dishwasher- Maybe think of using only plastic or metal ones whenever you make something for school?