I guess it depends on each child. My son is diagnosed ADHD and even when I'm teaching him 1-on-1 he keeps moving some part of his body or change his posture frequently. It bothered me before, but I learned that for him it's actually easier to work on the task. Restricting movement seems to make some part of his brain hyperfocused and in a short period of time his brain "shuts down".
In his school, the classroom is a kind of free style and although he has assigned desk he can choose other places to work on his task, which seems to help him a lot. (It's Montessori, so most of the time each kid works independently according to his/her own study plan.)
In his school, the classroom is a kind of free style and although he has assigned desk he can choose other places to work on his task, which seems to help him a lot. (It's Montessori, so most of the time each kid works independently according to his/her own study plan.)