Depending on the child, at nine he may be well aware of his relative strengths and weaknesses. One approach might be to have a supportive discussion with your child in advance, opening with a relative strength, bringing up the area of relative weakness, and getting his perspective on the situation... possibly he's noticed (or not), possibly he feels badly (or shrugs it off), possibly he'd like help (or may feel too vulnerable to address it directly and be part of a discussion with anyone but the parent). A kid might benefit from knowing that others have the same difficulties, in fact so many kids do that there are tests to see what can be done next.
This type of gentle probing, fact gathering, and reassurance that your child is not alone may help show the child that the parent is firmly on the child's side, build a foundation for open communication of difficult subjects, and demonstrate that the parent does not hold any weakness/imperfection against the child. (We all have foibles, some just learn about theirs earlier and gain more support in dealing with them.) Having this type of conversation may help determine the best way to proceed with the pediatrician. For example, while the parent has observed the outward differences, possibly the child would like to share his inner experiences of these differences with the pediatrician. This could build a foundation of trust, a sense of being part of a support team, and encourage eventual self-advocacy for the child.
