Kevin and Max discover their similarities as their friendship grows and certainly when they become Freak the Mighty. Imagining themselves as knights, they both enjoy the idea of helping people.
Until they met, Freak had limited physical ability and Max had a stifled intellectual past. In Chapter 7, when Blade and his gang chase them, they have to rely on Max's physical strength and Kevin's mental ability to completely escape. Max physically gets them away but Kevin thinks to whistle which alerts the policeman and saves them from Blade and from sinking into the mud at the bottom of the pond. So, you could say one big similarity is that they need each other, they need friendship, and each is better because of it. Alone, each is limited. And when Max is alone, he broods and feels useless. Together, they are both confident, helpful, and full of life.
Chapter 7 is when Max and Kevin realize that they can work together for the benefit of both their sakes. Tony D. is a boy who threatens them with a knife after the fireworks on Independence Day. Max and Kevin are similar because to boys like Tony D., they are easy targets for bullying. Because they are socially awkward and physically different, Tony and his gang think preying on Max and Freak will automatically be scared of them. Fortunately, Max has the physical strength and Kevin has the brains of the operation; so, they become one unified team against the bullies.
Max and Kevin are also similar because they are young, pre-teens striving to fit into a world who sees them as different. They both have feelings, dreams and goals that they want to achieve in a world that thinks they are not capable of doing normal things. This incident with the bullies, though, shows them that together they can do more together than they ever did separately. Max claims the following:
"That's how it started, really, how we got to be Freak the Mighty, slaying dragons and fools and walking high above the world" (40).