The kids do well if they can vs if they want to, to me is based off how well we as teachers can reach our students and find a way that they can learn that works for them. While giving them everything they need to be successful. If we go with the "if they wanna" mentality then they will not grow as students. It gives them an option of not doing work or learning. "If they can," we are helping them break through barriers to achieve a certain standard.
