It isn't. 70% of
cases of ADHD
have one or more comorbid neurodevelopmental
or psychiatric disorder. ADHD is an "Other Health Impairment" eligible for classroom modifications under Section 504 of the ADA.
3-tiered Response To Intervention is for kids with lower & slower academic progress. Evaluation for an Individualized Educational Plan under IDEA determines needed changes in curriculum when RTI doesn't help