Thanks everyone! Curious to know if others have seen a discrepancy like this?
Yes. DD had a similar discrepancy when tested on the EXPLORE as a 3rd grader.
Personally, I chalked it up to never being accelerated, but reading extensively from an early age (I believe her reading habits may have built her language skills). Also, when later tested on the WISC, she had an extremely high VCI (which may correlate with her extreme performance on the English subsection).
I have to admit that we never really considered the fact that DD, up until that time, hadn't spent the same amount of time on math skills as she naturally did on reading skills (because she LOVED to read). Since that time, we have been careful to offer her equal opportunity to develop both skills and we've seen her math skills develop in giant leaps.