Gerry Foley, principle of Belvedere College, where Jack went to secondary school, says no matter how big the roles get the Wicklow native will not allow fame and fortune to go to his head.
"He is no prima donna," Mr Foley told the Herald. "He may be in the biggest blockbusters in the world but he'll always be the same old Jack."
And the roles are certainly getting bigger for Reynor.
The 20-year-old has gone from small budget indie films to bagging lead roles in two massive blockbuster in the matter of a few months.
Principal Foley says Reynor's love of acting was apparent from a young age.
The What Richard Did star enrolled at the prestigious Belvedere College, Dublin, in 2004 and it wasn't long before he was treading the boards at the school's drama club.
"We have four major productions a year and Jack was always very involved in them," Mr Foley says. "He was so committed that even when he wasn't the lead role, he would always showed a variety, range and strength on stage."
Reynor has certainly fast-tracked his way to LA after catching the attention of movie execs when he stared in Lenny Abrahamson's controversial film What Richard Did.
Jack, who is nominated for a best actor IFTA said that his education at Belvedere helped him to connect with his character Richard. "I was brought up in Co Wicklow and when I was 12, I went to school to Belvedere, a school that was similar to those guys," he said.
Jack was then snapped up by legendary director Steven Spielberg to star in up-coming comedy The Delivery Man alongside Vince Vaughan.
And now he's bulking up for the lead role in Michael Bay's fourth Transformers film after he was handpicked by the director to replace Shia Labeouf in the popular film franchise.