In 2009 at the Under 19 National Championships, Alexander helped Harbour finish in third place. In 2010 at the Under 21 National Championships, he led Harbour to the title while earning Tournament MVP honours. At the Under 21 National Championships in 2011, he helped Waikato finish in third place while earning all-tournament team honours. In 2013 at the Under 23 National Championships, he led North Harbour to the title while earning all-tournament team honours.
