"He wants to entertain," says his mother.
As CBS News Correspondent Mika Brzezinski reports, he's a winning combination of class clown and good student.
So it's hard to believe that at age 3, life with Leo was a living hell. His behavior was so bad that day care was not an option.
"The shortest time on record at day care was three hours before they called me and asked me to pick him up and said he would not be welcome back," says his mother Kristen Massman.
Massman couldn't understand why her son was so miserable.
"He would break furniture, hit his head against the wall continuously," she recalls. "He would destroy his bedroom.
"I just did not enjoy being a mother."
Then at age 5, Leo was diagnosed with Attention Deficit Hyperactivity Disorder, or ADHA.
He was prescribed the stimulant Aderol. Instead of helping Leo, Massman says it made her son worse.
Leo was misdiagnosed. What seemed to be garden variety ADHD turned out to be bipolar disorder, which has many of the same symptoms.
"It's an easy mistake to make and it's made all the time," says Dr. Dimitri Papolos.
Papolos, author of "The Bipolar Child", says this kind of misdiagnosis is a growing problem, because the medications for ADHD can be a prescription for disaster if a child is actually bipolar.
"They could be aggressive to themselves," says Papolos. "They could make a suicide attempt.
"Things spiral out of control."
His doctor believes stimulants caused Leo to spiral out of control, culminating in a horrifying crisis point.
"I was bringing him home from school. I opened the back door to help him out and he just took off and threw himself in front of an oncoming car," says his mother.
"I remember sitting in the grass and holding him and saying "Why are you doing this? I don't understood what's wrong with you.'"
Leo is now on lithium, a mood stabilizer.
"I take these two in the afternoon, (and) all three of these in the morning," says Leo, showing his pills.
"Keeping him happy now is much more important and could potentially prolong, you know, his life rather than losing him," says Massman.
His life has turned around. His mother says all because of a clear diagnosis - one many doctors are reluctant to make. But for her and her son it was a lifesaver.
"It feels wonderful. I enjoy him now. I love being a mother. I love being his mother," says Massman
Though he is closely monitored at home and at school, his mother says the fear is just about gone. And Leo's life has finally, truly begun.