The Roxbury, Mass., native, who didn't play organized basketball until his freshman year at Charlestown High (Mass.), left the east coast about a year ago to play at Fremont High in California.
He went from national obscurity to someone that is among the most sought-after players on the west coast.
The 6-foot-7, 225-pound Gillenwater admits he was far from a model child in elementary and middle school.
``Going to Charlestown High was good for me," he said. "It gave me a chance to play on a real team."
Gillenwater, who turns 18 in December, played on the JV team as a freshman and moved up to varsity his sophomore season.
``I didn't get too much playing time and Coach (Jack) O'Brien kicked me off the team because I was in such a rush," Gillenwater said. "He was right. I wanted the ball all the time and I felt like I could help."
``He told me to wait my turn, but one day he brought me down to the locker room and told me I was off the team," Gillenwater added. ``You need to find yourself."
Gillenwater has done that 3,000 miles away after his old AAU coach, Greg Jackson, recommended that he and a couple of other local players head to California for more exposure.
``I was hurt when I was kicked off the team," Gillenwater recalled. "I was crying because I wanted to finish my career at Charlestown."
``But it was the best thing that could have happened to me looking back on it," he added.
Gillenwater thrived while at Fremont High – as a player and as a leader. He scored 37 points and grabbed 10 boards in a game against state power Crenshaw High.
However, just prior to the playoffs, it came out that the team's season was over because Gillenwater and his other teammates were deemed ineligible because they moved without their families.
``If that didn't happen, I would have finished the two years at Fremont," he said.
Now Gillenwater is headed to Stoneridge Prep (Calif.) after putting up 19 points and 10 boards per game at Fremont and also establishing himself on the national map this past summer with H-Squad.
``Rick (Isaac) gave me a lot of opportunities to showcase myself," Gillenwater said. "I know I still have a lot of work to do. My jump shot needs to be more consistent and my form needs to be better."
``This is my first year actually playing in AAU," he added. " ``I want to know what I need to do to be better," he added. "Tell me because I want to be one of the top players. I know my shot needs to be better and I need to work on my handle. I don't want to be a one-dimensional player that posts up all the time. I want to be versatile – like Michael Beasley. He can do everything."
Gillenwater has gone from someone that, a year ago, didn't have any colleges looking at him to a player who is being recruited by the likes of Illinois, USC, Kansas, Washington, Arizona, Texas, Kansas State and Oklahoma State. He said that he recently fielded scholarship offers from Kansas State and Oklahoma State to go along with his first offer from USC.
``When I was at Charlestown, I was lucky if I got looked at by a Division 3 school," Gillenwater said. "I'm just happy. It's crazy for me." ``I never thought this would all happen," he added. "That's why I am working so hard – because I don't want to disappoint anyone who has helped me."