My son was an absolute horror when bored at school. [G&T, Aspie & ADHD]
He was allowed to 'enrich' by using the library and online resources to expand what he had already completed in class. He did have oversight from science teachers to check his ideas for additional experiments he wanted to explore.
His school saught input from Ed Psych's to help head off boredom as he would walk out of lessons if they taught something he already knew. It was very tough for the first three years at secondary. We were all advised by Ed Psychs and NAGC not to push and let him be the lead and ask for what he felt he needed when he felt he needed it.
To begin with he just moped and moaned about boredom, then he gradually joined special interest lunch-clubs and would occasionally ask to head off to G&T events his school told him about. Over time he lost interest in the G&T events and began to ask for either extra work or permission to head off and self study further which he found far more fun.
Things became a lot easier after he made his options choices as it was he who camped outside the headteachers office refussing to move from the spot unless the head agreed he could do maths, stats,all three sciences, a BTec in Engineering and an additional BTec in software in addition to computer studies english and product design.
I think many schools are a bit wary of teenage hormonal years clashing with parental expectations and hopes. If it had been me going in and pushing the school I doubt things would have changed. I can honestly say my sons secondary really pulled out the stops when it was clear it was my son doing the pushing to be allowed to research and create an enriched circuluum. I just backed his corner when the head asked me if I thought my son understood how much extra work he was asking to take on.
[My son left school last June, he rejected the school pushing University at him and went via the Advanced Apprentice route. His years of learning to self advocate along with being G&T paid off. He now gets paid silly money for p/t work and silly money to study his degree. All his uni costs and tution fees are being paid for by his employer.]
As your son is now in year 8 perhaps this would be a good time to encourage and ask his ideas on what he thinks would help him to work towards a solution he could then suggest to his teachers/ head of year. Whilst it can be a tough ask of a 12-13yr old the skills they pick up as they begin to self-advocate and cope with frustration and boredom through the school system can really help when they hit the questions of what happens to them after yr 13.