Dear Searching,
There are Post Graduate schools often called the 13th grade. They offer additional preparation for students who struggled in prep school. Just Google "Post Graduate Schools" for listings. I believe one must take into consideration the individual circumstances surrounding a students level of achievement. For instance, the US government's mandated schooling was modeled after old Prussian Germany's socialist program which is designed to mold and control humans. Some children suffer dramatically to the prison like environment of the American classroom. If you evaluate closely you'll see that "most" students lack the ability to "think" for themselves. We are born into a system that forces us to be removed from the nurturing of our mother's far to early (most times as early as 4 years) told to sit down and shut up. Removing all forms of natural learning and creativity. In the end we become products of the environment and we also hand over our babies, continuing this dreadful evolution. Do everything you can to help your child out of this mess while understanding for the most part its not entirely his fault! You should research the history of the American school yourself. For starters Google "The Underground History of American Education" by John Taylor Gatto.
GOD BLESS