At our children's elementary school, the administration made it clear that parents were not particularly welcome to visit their children’s classrooms, although occasional visits would be possible if special arrangements were made several days in advance.
Not long afterward, the school sent home a pamphlet about choosing daycare, in which it was stated that under no circumstances should children be in a daycare situation in which parents could not drop in at any time, without warning. If such visits were not allowed, the pamphlet warned, parents should suspect that the daycare provider had something to hide.
As far as I know, no one in the school’s administration appreciated the irony.