"Teimana is a highly-focused and a totally committed player who brings physicality, aggression and a passion to his game which belies his size and off field manner," said Grinter.
"He has developed impressively over the years since his school playing days and he looks to have become the consummate professional with a long and successful international career ahead of him.
"I am over the moon for him and his family and those in the community that he carries in his heart whenever he plays as he builds his reputation in international rugby.
"He is a very special young man and talent who has seized opportunities to indeed reach for the stars."
Harrison, who started his early days as a lock, can now play across the back row and Northampton director of rugby Jim Mallinder believes he is ready for the step up to international rugby after a breakthrough season with Saints.
"He is definitely in the frame," Mallinder said recently. "He has been improving for a few years but I think we have seen a level of consistent performance from him this year to suggest that he go on and play at a higher level."
Harrison is one of eight uncapped players in the squad who will begin preparations for the one-off test against Wales at Twickenham on May 29 before the three-test tour to Australia. And Grinter believes Harrison's rise to the international stage will be an inspiration for all the current and future players at Rotorua Boys' High School.
"He certainly is someone to look up to for our boys. He shows that through hard work and a willingness to plan and prepare you can make it to the top," he said.
"Teimana still has brothers at school and as a recent leaver he is still well known around here by the current pupils.
"We can't wait to see him run on to the field in the white jersey of England."
