Is he able to do the work? That would be the most significant thing here. He may just be restless at this age & not able to focus well. That alone isn't much of a concern.
If he is unable to do the work, his behavior can be a way to deflect from that, as it's stressful to be in a situation where you cannot do what is being asked of you. If the work is too easy, it will also likely loose his attention, as it's not stimulating. That all said, he could also just have a hard time sitting still. I did. I was always a good student & even now I laugh if I look through old papers & show my children because every report from school says how wonderful I am in disposition yet I lack "any self control" and it was totally true. As I got older I learned to draw at my desk quietly if I couldn't focus on what was happening, but I still struggled with focus, but my grades were always great despite all of that.
I also think you can talk to the school & try to get them to work on strategies that help him, but ultimately, the school had to handle school issues. I do not personally believe that in an otherwise good home, there is a way to fix what happens in a classroom. Of course if a child is behind in school & needs help, parents can help or hire a tutor. If a child is from a chaotic home, that will harm them often in their focus & studies. But if home is good, generally, the school has to find strategies to implement in a classroom. They are supposed to be the experts here in how to handle a classroom with children of all different needs. I see it like I would never ask the school to help me sort out discipline issues at home. That isn't their time with my child, so how could they be the ones to answer that problem?
I am curious as to how it was decided that he needs someone from home there at lunch time. I have never heard of this situation with any child. All kids I have known have their allotted time to eat. If they opt not to eat, then they are just going to be hungry & typically a child will sort out they don't want to spend the afternoon hungry & decide they will eat during lunch period.