David Levine, a law professor at University of California Hastings School of Law, said the whole aim of the juvenile justice system is rehabilitation and the point of a fitness hearing is to determine if that's possible for a defendant.
"The idea is that whatever crimes these people have committed, the hope is they can be rehabilitated, returned to their communities and returned to their families," he said.
Prior to the 19th century, Levine said, common held that anyone below the age of 7 was an infant and everyone else was an adult. Sometime in the 19th century, Levine said, popular opinion changed as people realized children aren't fully formed adults and that it's appropriate to treat them differently.
Where things get a bit complicated, according to Levine, is when you have a child defendant who stands accused of a horribly violent offense. States deal with the situation differently, but all have some mechanism that allows juveniles to be tried as adults for certain offenses and it is estimated that about a quarter of a million are prosecuted as adults each year, according to the Juvenile Law Center.