It depends on where your child is seated in the classroom and your child’s age, but for children aged 9 and above, you should start thinking of buying spectacles for them when their naked-eye vision hits 0.5, and 0.2 to 0.3 is the degree level that requires spectacles.
If they keep going without spectacles, it might hinder their studies. Wearing and removing spectacles repeatedly does not cause myopia to worsen.