One formula from reading research explains a surprising number of real-world reading struggles: Reading Comprehension = Decoding × Language Comprehension. Multiplication, not addition — and that changes everything.
Why multiplication, not addition
If reading were decoding plus comprehension, a child strong in one could partly compensate for weakness in the other. But it's decoding times comprehension — and anything multiplied by zero is zero. A child who decodes every word perfectly but doesn't understand the language it's written in still won't understand the text. A child with rich vocabulary and understanding but no decoding skill can't get into the text at all.
The profile this explains: strong decoder, weak comprehender
This is one of the most commonly missed profiles: a child reads words accurately and even fluently, but struggles to explain what they just read. Phonics practice alone won't fix this — the gap is on the comprehension side (vocabulary, background knowledge, understanding sentence structure), not the decoding side.
This is why phonics is necessary but not sufficient
Phonics builds the decoding half of the equation extremely well — but it's still only half. A reading plan that's 100% phonics with no attention to vocabulary, read-alouds, and discussing what's read will eventually plateau. See our guide to what comes after phonics for how the two sides come together in practice.
For a richer picture of everything that feeds into the comprehension side specifically, see Scarborough's Reading Rope, which breaks both strands into their component skills.
Not sure where to start?
Build a free personalised phonics practice plan for your child — pick a start date and pace, we schedule the rest.