Bit long, and this is only the highlight of what I could say on this topic!
Schools only have so much time and money, and only so many teachers and support staff etc. They are judged on how many children reach certain targets. This means that extra support is often focused on children who are just below the target and have a good chance of reaching it, because they are the ones who make the most impact on the school’s numbers.
The problem is that children who are struggling and are well behaved can be the ones who most easily miss out. They don’t cause problems, don’t demand attention and can appear to be coping when actually they are not. With limited resources they can become almost invisible. They may need far more help than what is available, but because they are unlikely to reach the target, they get more of a “make do with what is left” approach.
They don’t leave children like your son to fail. With limited resources, it is more damage limitation. So, for those who struggle a bit more, it can end up meaning they settle for showing they have made progress, even though that “progress” is not them reaching their full potential. Every year these children remain behind, it can become harder to catch up.
Many children struggle initially for no reason other than that it takes them a little longer to get going. Some are later diagnosed with an SpLD such as dyslexia. The main thing is not to panic. There is still time for your son to reach his potential, but I would act now. Get him assessed and consider a tutor. Not an academic hothouse trying to push him through endless extra work, but someone who can understand where he is struggling and help him access learning in a way that works for him.
Get the right support now, whether that is a specific piece of support that gets him back on track or more long term help, and your son has every chance of becoming a much happier and more confident learner. Talk about people you know or other successful people who have had challenges. If it is dyslexia, for example, Richard Rogers the architect and Lewis Hamilton. Normalise the fact that not everyone learns in the same way or at the same speed. Your son might not be dyslexic, but you get my drift. If he understands that struggling with something at school does not define his intelligence or what he is capable of, he is much more likely to believe that it is worth putting in the work because he has choices and can decide the direction of his own life.
Education should be about helping children access opportunities, not sending them the message that their value as a person is measured by their GCSE grades. I think schools, in trying to do their best, can reinforce the message that your value is your grade.