Start with the myth, because it sends families down the wrong road every day: reversed letters are not the signature of dyslexia. Nearly all young children reverse b/d and write mirror letters into first grade; it's a normal stage of visual development. A seven-year-old writing "bog" for "dog" is unremarkable. The signs that matter are quieter and show up earlier.
Signs worth noticing, by age
Preschool (3–5): trouble learning nursery rhymes or hearing rhyme at all; difficulty learning letter names (not writing them); mixing up word sounds ("aminal," "pasghetti") past the cute stage; family history of reading difficulty — the single strongest early predictor.
K–1st grade: can't reliably connect letters to sounds despite instruction; can't blend sounds into a word (c-a-t stays three sounds); guesses words from the first letter or the picture; reading is effortful in a way classmates' isn't.
2nd grade and up: reads slowly and laboriously while listening comprehension is strong; spelling is dramatically worse than reading; avoids reading aloud; knows a word on one page and misses it on the next; homework fatigue out of proportion to the assignment.
The through-line isn't reversals — it's effort that doesn't convert into automaticity. Typically developing readers get smoother every month. A child at risk for dyslexia keeps paying full price for every word.
When to test
The research answer is clear: don't wait. The "wait and see if he grows out of it" year is the most expensive year in a struggling reader's life — intervention in K–2 is dramatically more efficient than the same intervention at age ten, and by then the self-image damage is compounding. If the signs above are present and persistent for more than a school term, testing is warranted. You don't need a teacher's permission or a formal referral to start.
What testing should include
A dyslexia screener that only samples phonological awareness answers only one question. As we covered in what a reading assessment actually measures, a complete evaluation looks at decoding strategy, eye movement and teaming, mental imagery, language foundations, and attention/stamina — because dyslexia-like symptoms can come from several different systems, and each points to a different intervention. Some children who arrive with "probably dyslexia" turn out to have a highly workable visual or imagery bottleneck instead; some have dyslexia and a visual overlay, and remediating both is what finally moves the needle.
Either finding is good news, because both are addressable — and finding out is one afternoon.
Our dyslexia overview explains the developmental lens, the science page covers the research, and our reading page describes the full evaluation. If you're seeing your child in this post, the Clarity Assessment is the next step.