The half ended as it started with Corpus Christi adding a third try, and a second to the lively Jarrett, and Sheedy's conversion made it 24-12 to the Cardiff-based team at the break.
But a stunning burst of three tries, and 21 points, in 10 minutes after the break from Caerleon turning the game on its head and gave them the momentum. Curtis Avery, Wales Under 16 centre Tyler Morgan and Seamus Clancy all crossed and Thomas improved all three scores to make it 33-24 to his team.
Corpus Christi cut the gap to two points with their fourth try on 54 minutes, this time from wing James McLean, and the same player had a chance to put his side ahead eight minutes later after a neat chip over the top. This time, though, he knocked-on in the act of scoring.
Caerleon hit back through the impressive and increasingly influential Morgan, who charged down a chip ahead to allow Seamus Casey to pick up the pieces and score and then scored his second try after another charge down.
In the Welsh School Under 14 final Gowerton stopped Glantaf making it a double after their triumph in the Under 18 final as they triumphed 24-17.