In terms of UoM, this year they took kids with 55 GAMSATs and 5.5 GPAs, which is extremely low (relatively). It's going up next year without a doubt, due to a few factors.
In general, anything over 60 in the GAMSAT is competitive, anything over 70 will get you to the interview. UoM calculates GAMSAT scores differently to the rest of the country though, they like to be special :S
the justice of peace is i'm pretty sure only for those not attending school/dont have someone to sign for them like school can do
Your principal is equivalent to a JP in terms of signing/authing stuff.
@Stonecold: GAMSAT isn't thaat scary, compared to the UMAT I'd say it's actually more enjoyable sheerly because the questions won't leave you scratching your head and saying "wtf". But relatively, it's obviously at a higher academic level.
but hey, I just love reading/writing so SI and SII were my favourite