Since nearly half of children, adolescents and adults with ADHD also have learning disabilities, it would be important to find out if you also have a learning disability. Yes, being inattentive or impulsive can interfere with test taking. So too can difficulty with reading comprehension, organization, memory, or being able to get your thoughts onto a page.
Discuss your problem with the person who diagnosed your ADHD. If your test problems are because of your ADHD, you should be on medication and your school should provide appropriate accommodations – for example, extended time on a test. If you also have a learning disability, you will need special educational help to learn to compensate for these problems.
Accommodations on the SAT