Jack (Robin Williams) is a 10 year-old boy who was born with a condition that causes his body to age four times faster than normal. Though Jack lives in a child’s world, he occupies an adult’s body. His parents, Brian (Brian Kerwin) and Karen (Diane Lane), and private tutor Mr. Woodruff (Bill Cosby) have kept Jack sheltered from the outside world. But Jack wants to live as an ordinary child. With dreams of going to school and being with other kids his age, Jack finally embarks on the greatest adventure of his life-the fifth grade.