My son was similar in primary school, and honestly the earlier you work with his teacher and PD the better, because they can help put support in place before secondary school kicks in. A few of my mum friends found that once their kids got proper strategies at home and in class, things improved a lot by the time they hit upper primary. I'd suggest chatting with both the school and your PD about what accommodations or techniques might help him focus during lessons, because every kid is different and what works depends on understanding how his brain works best. The good news is that with the right support system early, many kids do really well academically despite ADHD.