I am not sure what schools you are looking at for high school and their entrance requirements but it certainly isn't too late to turn things around. You have a few weeks across the summer holidays to talk with your son and figure some stuff out. Maybe make some time for chat dates over his favourite food or ice cream and be gentle. If he was making moves to find a solution to what he viewed as a problem and moved away from his friends, then he is looking for a way forward. Take that as your approach. Maybe start with, how do you feel school went this year? Take a collaborative approach. Look at his school work with him and see if there is a pattern to any problems. Is he missing any steps or knowledge. Tutoring will help. Take along copies of his NAPLAN results, the detailed page with every question on it. Tutors can see the patterns in any areas he might need help or extension as you mentioned he did well on the national testing.
Authoritative isn't authoritarian. Authoritarian implies strict rules, punishment for failure but with little respect for the child's opinions. Authoritative parenting also sets clear expectations and guidelines, but you have open discussion with your child. It is about being responsive, involved and supportive. Kids like to know what the boundaries and expectations are and how to meet them. If they don't meet them you need ways to help them meet them. There need to be consequences but necessarily just punishment. The consequences need to support the desired behaviour.
When DD didn't achieve results she, or I, expected in a class test, we talked about why that happened and a positive way forward. We discussed the need to replace screen time with bursts of study. We figured out that she studied better in certain ways that matched her visual style and worked on those. My job was to remind her to turn off the TV and why, so she could meet goals she had set. I made sure she ate and drank before studying and provided any materials she needed.
Talk with and work with your son. Let him know you are in this together. Pinpoint what he needs and help him set good goals and meet them. Don't expect perfection, it doesn't exist. Be realistic about the battles you pick, stick to what is most important to both of you. Make it a shared journey.
