I'm going to be honest with you. His grades right now won't cut it for north sydney boys if he is getting Bs and Cs. Cut off for North Sydney is at 231 right now, and that's into reserve zone where you do not want to be, to be safe, 240 is needed. This equates to approximately 80% across the selective papers which is distinction or higher in ICAS English and Maths, and mostly A range, maybe B's if the primary school ranks high (not equal tests to the selective test by any means, but approximate comparisons).
However there is hope. Your son should have about another half a year before the selective test. Given that he does indeed have the ability to make selective, well-aimed and plentiful prep would get him in.
Also keep in mind that partial selective schools often drop into the 180s range from entry scores. That's about 60% on the actual test paper, which should be doable for anyone if they try.
Now for 240+ onwards in selective, there's two main problems:
1. Maturity/discipline
2. Intelligence
Either can be compensated by the other. If either are lacking, some forcing needs to be done to study more.
50/100 is a totally fair school mark for most students it is given to. The school mark is meant to emulate what the student can score on the actual test, and many do not pass.
For reference to cutoffs for schools (which are pretty consistent), refer to
https://www.north-shore.com.au/blog/selective-cutoffs-2020/. Add 5 points on for direct entry. These marks are for the reserves who got in after people who had direct entry rejected the offer.
Personally, I remember that I had no semblance of a direct and logical train of thought which is required to do selective questions quickly and well. Training a kid to do something results in them forgetting the method LOL.
Only way to attack the selective tests well imo is to 1. know the prerequisite knowledge (can be understood from looking at papers), 2. a crap tonne of experience from getting things wrong over and over again and understanding why you got it wrong. (at some point you just get tired of getting it wrong). 3. A fair bit of testing technique (which can come from practice) or be taught. e.g. draw out the alphabet, learn to eliminate improbable answers, know how to test the multiple choice answers. 4. The kid should also be personally invested into making it into a selective school, but not too worried (causes stress and choking on exam day).
*Just one more thing. The kid's vocabulary needs to be consciously built, or else you get screwed over in GA, writing and English which is a huge yikes.
As for the travel issue, I disagree with quickoats. While it does not ensure as comfortable an experience, spending a crap tonne of time travelling is not without its benefits.
1. Time management skills (you don't have as much time to waste when you get home).
2. The kid has to travel home at a reasonable time and thus doesn't have as much time to do dodgy stuff, if he is likely to stray in that direction.