We knew to test my brother for dyslexia in pre-k when he spelled his name completely backwards, nhoj, on a homework assignment.
Dyslexia is not a synonym for stupidity, as most dyslexics have high IQ scores. It is also not a made-up 'excuse', as MRI scans of dyslexic people have found that their brains are shaped differently to those of most people, with the language area in the right hemisphere being the same size as the language area in the left. (In people without dyslexia, the left language processing area is much larger than the one in the right hemisphere.)
Dyslexic people are often particularly gifted in art, music, sport, drama, or anything involving visual creativity. Some are also talented authors - the awardwinning poet Benjamin Zephaniah is dyslexic.