Despite being Canterbury and South Island champions, co-coach Jack Williamson said they may still be able to fly under the radar.
The nationals begin on September 30 at Palmerston North with Cashmere High School, St Andrew's College and Shirley Boys' High School the other Christchurch schools competing.
"Not too many of the teams up there would have seen us before and I'm hoping that when they see how under-sized and un-athletic looking we are during warm-ups that they may take us lightly," he said.
Middleton Grange have simply run their South Island opposition off the court all year and their multiple outside shooting threats have proved too hot to handle so far.
Williamson said they were keen to keep playing that style of game.
"We know the North Island teams will be more physical than what we are used too but we will just try to play our way that has worked so well for us so far.
"I thought the team got better as the (South Island) tournament went on and hopefully we can build on that."
Middleton Grange managed their third win over former South Island champions Cashmere High School in the semifinals of the tournament in Nelson but Williamson said they would still be a threat at nationals.
"Our style works for us against them but they have some big bodies and talented players so we still expect them to do some damage at nationals."
Williamson said the coaching staff were hopeful of making the top eight and then seeing how things go from there.
