Two children start school almost level. One is in a book-rich, stable home; the other has less support around them. Watch what an ordinary decade does to a gap that starts tiny. The difference is in their surroundings, not in the children.
How to read it: each line is one child's skill level, from age 6 (left) to 16 (right). Use the button under the chart to step through what happens.
Well-supported childLess-supported childOne-off boost at age 9Sustained support from age 9
The gap was built by the environment, over years, not by the children. A tiny early difference compounds because being a little ahead makes the next step easier. A one-off boost fades, because nothing keeps feeding it. Sustained support later still closes the gap, because the compounding runs through the environment across time. That is why "early matters" is not "the die is cast": early conditions echo, but the window never fully shuts, and what decides the outcome is whether the surroundings keep building on the gain.