Do you have subtest scores?

Is your child bi-lingual? Any issues you area aware of with hearing or speech? Did the tester have a strong accent that your child wasn't used to?

A big gap like this is often a flag for a learning disability or some other issue, but there are other factors that can cause this kind of a result. Knowing the pattern of subtest scores (Were there three 10's, or two 14's and a 2?) can sometime help you figure out where to look for the cause.