How is the character of david petrakis a juxtaposition to melinda in speak?

David is a brainiac and one of the few people who treats Melinda decently. He's in Melinda's social studies class and is her lab partner in biology. It's not clear how much David suspects about Melinda's problems, but it seems likely he's aware things aren't right with her. His protectiveness toward her, his gentle but strong urgings that she speak her mind - these suggest he really cares about her.