The post from ckw makes a lot of sense.
States develop criteria for identifying children with disabilities.
I would suggest that Beth may want to talk to her state special ed office and get criteria for LD and for steps to get an initial assessment, as again, these vary by state. I do agree with her that a child can have significant skills in one area and still have a learning disability. So, he may indeed have a learning disability, or perhaps this is maturational and he will gain the skills as he grows. A good assessment will help determine this. Good luck in getting what your son needs to help his progress.