Following a line of direction with the eyes may be a problem for some children.
I never could resolve the two so I switched to teaching my sons chess, which I could handle visually if not mentally.
For a teacher in a classroom, I think it would be an interesting activity to test the students' ability to focus between the blackboard and their desks.
For example, a bingo type game might be adapted for this purpose. Students could match a number put on the board with a card on the desk .
The teachers could time their responses and perhaps detect a potential problem here and there.
Tracking: This is the ability of the eyes to follow a line of movement. Actually, there are two considerations here. Can the eyes track a moving object; and can they do it together.
A somewhat quick, if not highly sensitive, screening test can be conducted in the classroom.
NOTES: See a review of some visual problems in children.