A contract under this chapter shall continue in force and the care, maintenance and education provided therein shall continue until such child who is blind attains the age of 8 years. The State Board of Education may, however, cancel such contract and remove such child who is blind from the institution or school if, in its judgment, such child who is blind does not improve in such a way as to warrant its continuing in the same, or extend the time if the progress of the child requires a longer stay.