That split in skills is what I was looking for... some kids are highly gifted in reading, and struggle with both math and writing... in which case, there's a higher chance of something like a motor skills disability such as Developmental Coordination Disorder (DCD). But that doesn't sound likely in this case, given the success with writing.
Not sure exactly what qualifications are behind testing for that one... some schools test for the full range of LDs - others leave it to the medical side...
Do you have a Learning Disabilities Association? They are often a good source for testing... and/or can point you in the right direction.
