He was rushed to Christ Medical Center in Oak Lawn where he was pronounced dead just after midnight.
The game was part of a senior overnight lock-in function at the school.
Simmons was planning to attend college in the fall. Now his parents are mourning the loss of their son.
"You couldn't ask for a better child," said Paul Simmons Sr. "You know, I had no problems out of him. I loved him. His mother loved him. The whole family loved him. He was just -- I don't know how to explain it to you. He was just a good kid."
Paul Simmons Sr. is heartbroken, but so proud of his son Friday as he showed off some of the trophies, awards and photos of his 17-year-old child.
Paul Simmons Jr. was at school Thursday night for a senior lock-in. The overnight session was a special event just for graduating seniors. They were enjoying themselves.
Paul started to play basketball with his varsity teammates when he suddenly collapsed. He was rushed to Advocate Christ Hospital in Oak Lawn where he was pronounced dead just after midnight.
"Great teammate, kind, polite, compassionate, always thinks of others before himself, and our whole school is just in shock," said Marist High basketball coach Gene Nolan.
There is also sadness because Paul had big plans for the future. He was going to major in business and finance, as well as play basketball, at Spring Hill College in Alabama.
"His focus was on going on to college. He was talking over the last couple days with his senior classmates some of his senior classmates and his conversation was all about making something of himself and of helping others make something of themselves. So, he had a drive," said Marist High Principal Larry Tucker.
His family had also been looking ahead to that future. They had already given Paul his graduation gift.
"He liked people, he liked his car-- we got him a new car for his graduation," said mother Vera Angion. "He loved his family."
Late Friday afternoon, autopsy results determined Paul had a thickening of the heart muscle, which made it more difficult for his heart to pump blood.
His family is hoping other parents of young athletes will learn from Paul's death that the required sports physicals might not detect some potentially serious health problems.
