Mr. Freeman is your classic mentor. He not only helps Melinda find her inner-Picasso, but also becomes someone she can safely confide in. Even if their relationship ends, it's likely Melinda will use the things she's learning from Mr. Freeman all her life.
Melinda sees David as a role model. He guides her through biology class and through the ins and outs of the suffrage movement. He shows her what it looks like to stand up for your rights in school. David also shows us what it looks like if students have access to the legal system. David is able to speak his mind in school because a) his parents supported his actions, and b) because they were willing to hire a lawyer to protect his rights. Without access to the legal system, David probably would have become the target of a series of disciplinary measures, like many other kids who speak up in school, sometimes with tragic results.