20 / 70 eyesight

We decided to take Britanie to the eye doctor because she always has to sit in the front row to see the chalk board in school. And as most of you know....it is NOT 'cool' to sit in the front row. The doctor checks out her eyes and says she has 20 / 70 eyesight. You would think with this number....the eye doctor would have sent Britanie home with a prescription. NOPE!!! He said he had nothing that would help her see better. Is there something wrong with this scenario? We are definitely going for a second opinion.