What dyslexia is, in one paragraph
Dyslexia is a specific learning difference that makes it hard to connect the sounds of spoken language to the letters that represent them. It is not a problem with intelligence, vision, effort, or how much a child has been read to. It runs in families, it affects roughly one in five people to some degree, and it does not go away on its own. What does change, with the right instruction, is how well a child reads.
Because reading skills build in a predictable order, the signs of dyslexia change as a child gets older. A four-year-old who cannot rhyme, a first grader who guesses at words from the first letter, and a fifth grader who reads accurately but slowly and hates writing may all be showing the same underlying difference.
The thread that runs through every age
Whatever the age, the core difficulty is the same: hearing and working with the individual sounds in words, and then mapping those sounds to letters quickly and automatically. Younger children show it in speech and rhyme. School-age children show it in decoding and spelling. Older children show it in fluency, writing, and the exhaustion of keeping up. If you know what to look for, you can often see it long before a report card does.
If your child is bright and reading close to grade level but everything about reading and writing seems harder than it should be, read about stealth dyslexia too.