Claudio is less of a foil for Benedick than Hero is for Beatrice, but Claudio's conventionality, his immaturity, and his compliant behavior contrast sharply with Benedick's independent spirit, his jaded opinions about women, and his sense of humor. The reader/playgoer who loses patience with Claudio is glad to find a stronger, seemingly less pliant figure in Benedick.
Claudio was apparently attracted to Hero on an earlier visit, and on his return is completely captivated by her. He may also be looking longingly at what she stands to inherit as Leonato's only child, and what he could gain by being married to her when she does. He seems oblivious to Benedick's scathing remarks about her and his attitudes about marriage. Then he allows himself to be deceived by Don John, not just once, but twice. Later he realizes his mistake and allows himself to be deceived by Leonato in an effort to re-ingratiate himself to the family for his earlier error in denouncing Hero. Finally, he recovers himself completely to marry the original (but wiser?) Hero. Somehow, he has the presence of mind to have with him Benedick's love poem for Beatrice and to make it public at the right time.
Does Claudio change during the play? Not much, it seems. He is still immature, ready to concede to whatever marriage plan is presented to him, lucky that a forgiving Hero and her family will even accept him.