As many of you Percy Jackson fans know, the demigods can have ADHD and dyslexia. and a lot of them do. Can you explain why this is the case please? This is what bugs me the most.
From the Riordan wiki entry for ADHD
Most demigods are labeled as suffering from ADHD, but it is actually a sign of their heightened senses and natural aptitude for battle. ADHD also gives demigods greater battlefield reflexes and the ability to see where their opponents will strike due to the tensing of their muscles. It is usually coupled with dyslexia in demigods.
However, through the Percy Jackson and the Olympians series and beyond, Percy Jackson, along with other demigods, suffer from dyslexia. This is explained to Percy by Annabeth Chase, who informs him that their dyslexia is a result of demigods' brains being "hard-wired" to interpret Ancient Greek, not English. It is usually coupled with ADHD.
So, long story short, it's a natural consequence of their divine abilities. Their brains are wired for combat with heightened senses, so they're constantly noticing things about their environment, which distracts them, and their brains are wired for a language different from English, which makes comprehension difficult.
Out of universe, Rick Riordan's son, Haley Riordan, has both dyslexia and ADHD and he patterned Percy after his son.
When I was writing Percy Jackson, my own son was in the process of being tested for learning differences. He was having trouble reading, and some trouble focusing in the classroom. The teachers were wondering about ADHD and dyslexia. He was frustrated about learning to read, and we had to explain to him that the testing was designed to help the teachers help him, not to make him feel bad…. dyslexic/ADHD kids are creative, “outside-the-box” thinkers. They have to be, because they don’t see or solve problems the same way other kids do. In school, unfortunately, they are sometimes written off as lazy, unmotivated, rude, or even stupid. They aren’t. If they can get through their rough school years, they often go on to become very successful adults. Employers love them, because they come up with original, fresh ideas. Making Percy ADHD/dyslexic was my way of honoring the potential of all the kids I’ve known who have those conditions. It’s not a bad thing to be different. Sometimes, it’s the mark of being very, very talented. That’s what Percy discovers about himself in The Lightning Thief.
The book explains it as "heightened senses" (that's not a direct quote) so they are better on the battlefield. Personally I think that sounds very dumb (and I have it). Also, dyslexia was described by saying his mind was wired for Greek writing (also dumb) although it is a very good book series.
"Diagnosed with dyslexia. Probably ADHD, too."
I tried to swallow my embarrassment. "What does that have to do with anything?"
"Taken together, it's almost a sure sign. The letters float off the page when you read, right? That's because your brain is hardwired for ancient Greek. And the ADHD—you're impulsive, can't sit still in the classroom. That's your battlefield reflexes. In a real fight, they'd keep you alive. As for the attention problems, that's because you see too much, Percy, not too little. Your senses are better than a regular mortal's. Of course the teachers want you medicated. Most of them are monsters. They don't want you seeing them for what they are."
Percy Jackson & the Olympians, book 1: The Lighting Thief, chapter 6: "I Become Supreme Lord of the Bathroom"