When my son was about to move on to first grade, I visited the two local schools and their first grade classrooms. Each had the daily schedule on the blackboard and I noticed that they switched to a new activity every 20 minutes. I asked what if you have a child who wants to focus for longer on something. They said they individualize materials but had far too many children to individualize the schedule. There were times when my son would focus for 2 hours on something.