On 10 May 2016, he was included in the final South Africa Under-20 squad for the 2016 World Rugby Under 20 Championship tournament to be held in Manchester, England. He started their opening match in Pool C of the tournament as South Africa came from behind to beat Japan 59–19, and played off the bench in their next pool match as South Africa were beaten 13–19 by Argentina. He was restored to the starting line-up for their final pool match, as South Africa bounced back from their defeat to secure a 40-31 bonus-point victory over France to secure a semi-final place as the best runner-up in the competition. He started the semi-final, as South Africa faced three-time champions England. The hosts proving too strong for South Africa, knocking them out of the competition with a 39–17 victory. Jackson also started against Argentina in the third-place play-off match, but suffered their second defeat to Argentina in the tournament, convincingly being beaten 49–19 to finish in fourth place in the competition.