Tristan has a genetic disorder because of which he has an intellectual disability. his mother informs tristan's pediatrician that tristan has an extremely short attention span for any task. based on tristan's symptoms, the pediatrician is most likely to diagnose tristan with

ADHD and or ADD

Explanation:

I believe he has either one of those because ADHD is explanatory in the name itself, Attention-deficit hyperactivity disorder, whereas ADD stands for just Attention deficiency disorder, meaning that a lot of the times the individuals who have this have a very short attention span and can't focus, finding distractions to hinder themselves from the task at hand. I myself actually have ADD and have sought out help to allow me to focus on my schoolwork, and it's the best choice I've ever made!