Because you attend a small independent school, not a US public school, or one which receives government funds for any of its programming, the school may not be obligated to address learning disabilities/differences, special ed.

Remediation/accommodation which assist a child in developing skills to compensate for weaknesses are often provided in earlier grades. Developing study habits and organizational skills are crucial and may be taught/learned at home (not just in the classroom). The website Understood.org has lots of information on ADD/ADHD and executive function (EF).

Does the school currently have an advanced LA/SS/Science class or student cluster group which your son might join (to be placed with intellectual peers... or near-peers), or would you be asking your school to create something new for your child?