Are you sure your child has good vision?
Children with undiagnosed visual impairments are more likely to have academic difficulties . An eye exam can detect and prevent these difficulties.
Up to 41.8% of children in Catalonia show symptoms of having a vision problem that hinders their learning and 6.2% have an undetected visual defect (Statistics provided by the Official College of Opticians and Optometrists of Catalonia after a study in 197 schools, 6402 children http://www.coooc.org/noticia.asp?id_noticia=603 ).
It's not necessary for a child to be able to read to have an eye exam; the tests are done with images. It's recommended, just as with dental visits, that a child be examined once a year, starting at six months of age.