You are quite right about visual distractions. Follow your instinct on this. Sunlight glaring onto the blackboard can also be a forgotten interference.
Let me share my child's experience in what I consider the worst possible scenario. This was a split Grade Two/Three class of 72 students in a language immersion setting. A double classroom was divided with a floor-to-ceiling folding door. I'm sure you can imagine it.
Distractions were multi-sensory, but here are a few of them:
- Odors and noise from the adjoining school kitchen (recycling of beverage containers done during class time; juice boxes, etc. drained in kitchen, without thoroughly flushing/bleaching drains -- mold growing?)
- people shortcutting to the school kitchen through the classroom; even the principal did this, b/c the kitchen door was locked, but the classroom was not
- classroom door usually left open
- divider between classrooms usually left open
- classroom situated directly across the hall from entrance to the gym and music room (remember, the door was usually open)
- high volume of hallway traffic in school of nearly 550 students
- adjoining classroom had a piano, which was used when my son's class was learning science, etc.
- overcrowding; this double classroom held 44 students in previous year; my son's side had 38 students; children bumping into each other, chairs, desks
- not enough coathooks; coats, backpacks, snowpants, etc. thrown on floor
- Students split into A, B and C groups for various subject instruction throughout the day; subjects like Social Studies taught to split grades, despite widely varying curriculum
- little help for the students in core subjects due to a student-teacher ratio of 38/1 ratio in certain subjects
One of the greatest stresses came from the sheer noise of having so many children in such a small space, moving chairs on the floor, etc.
And of course, children in primary school should have a single teacher for optimum performance. Attachment to the teacher aids learning at this age. Instead, there was a complex schedule involving splitting the children up and moving around from classroom to classroom and teacher to teacher several times daily.
My advice is to avoid all of these distractions. I felt very sorry for the children and teachers in this situation, which was the disaster you might imagine.