 Jamieson didn't feature in any school provincial competitions for Eastern Province, but in 2013 – while still in the Under-18 age group, he was included in the squad that participated in Group B of the 2013 Under-19 Provincial Championship.He started four of their seven matches during the regular season, scoring a try in a 42–20 victory over the team to help his side finish in third position on the log to secure a semi-final spot.He started their 45–30 victory over in the semi-finals, as well as their 56–40 victory over the table-topping side in the final to help them secure the Group B title.