It's hard to know for certain. I agree that "deserves" makes a better advertising slogan, if they hope to persuade people to choose the school in the future.
It's possible that they had something else in mind. Perhaps they are congratulating parents on having chosen their school, and give this as the reason it was a good thing to do. [You sent your child to this school because you knew that] your child deserved the best.
I like Copyright's interpretation too.
Without context, we start making up our own, and go off in all directions.