What are some ways you can tell that Percy has ADHD?

Percy actually does not have ADHD.  This is something Annabeth explains to him once he arrives at Camp Half-Blood.  He's always been told that he has dyslexia, but Annabeth explains that he does not; it's just that his brain his hard-wired for ancient Greek writing, and so 21st-century American English simply doesn't compute correctly.  Also, Percy's always been described as impulsive and had a hard time sitting still in the classroom, but Annabeth explains that...

Percy actually does not have ADHD.  This is something Annabeth explains to him once he arrives at Camp Half-Blood.  He's always been told that he has dyslexia, but Annabeth explains that he does not; it's just that his brain his hard-wired for ancient Greek writing, and so 21st-century American English simply doesn't compute correctly.  Also, Percy's always been described as impulsive and had a hard time sitting still in the classroom, but Annabeth explains that these are his "battle-field reflexes" and not a lack of impulse control at all.  Finally, Annabeth tells Percy that another reason he seems to have attention problems is that he sees more than the average mortal, not less.  This is another reason he's been told he has ADHD.  She claims that most of the teachers are monsters, and this is one major reason that they'd want Percy on ADHD medicine: they don't want him to be able to see them for what they really are.