There's no right answer, it really depends on the child.
What I do in similar situations with my son who seems to ignore consequences is listen to the teacher and find out what exactly they know, then ask if there's anything they'd like me to do at home (the answer is always no) then I mention it to my son in an "oh dear" kind of way on the way home, but don't expect anything from him at that stage.
At home we have pre printed "sorry" cards where you can circle, draw and colour in red on a stick person what happened and how the other person felt, as well as a space to write what you'll do next time. We can get one out after he's had dinner, toilet and got ready for bed, as in his case that's when he's in listening mode more as he doesn't have any more demands for the day.
It was still good before he could write as we could fill it in together without any demand avoidance kicking in and out makes a visual record of what happened. Also it's quite positive as in how can he stop it next time, rather than punishment based. This works in place of punishment because he doesn't actually want to hurt children in the first place, it's usually a regulation issue, which punishment actually exacerbated. Discussing what to do instead helps more.
Then after filling it in he can take it to school and give it to the person as an apology if he wants, which he always does. I also separately report back to the teacher his explanation, as there's usually a "reason" why he did it. Then they can put things in place like he stays at the front of the queue or goes to the reading corner for 5 minutes after lunch rather than sitting on the carpet.
Yes on paper it sounds like it's consequence free, but it works, it maintains trust and takes the emotion out of it on my side, it gets the information needed for us to help him and him to help himself, and even the other child gets a proper rather than a forced apology. If your child sounds similar then you can take elements too.
We also have"thank you" and "ouch" cards to cover other situations, he can write them all himself now he's 6.