Once she realized that he was mentally disabled, Blair took it upon herself to tutor Leo about fine art and painting, in an effort of getting him to expand his mind and his talents.
Of course, Blair expected too much and pushed Leo too hard, which led to this:
After he ran off in tears, Mrs. Garrett gave Blair a stern talking-to about her unrealistic expectations. She urged Blair to learn to accept Leo for who he is, and not worry so much about who she thinks he should become.
Blair eventually apologizes to Leo and gets him to agree to paint her another picture. But instead of worrying about what she wants, Leo gets to paint it however he wants.
It was actually a touching episode. I really liked Leo and wished that we could have seen more of him in subsequent episodes. But like most very special episodes, we rarely get to follow up beyond that initial thirty minutes.