WASHINGTON (AP) — Sometime in elementary school, you quit counting your fingers and just know the answer.

Now, scientists have put youngsters into brain scanners to find out why, and watched how the brain reorganizes itself as kids learn math.

The take-home advice: drilling your kids on simple addition and multiplication may pay off.

Healthy children start making that switch between counting to what’s called fact retrieval when they’re 8 years old to 9 years old, when they’re still working on fundamental addition and subtraction.

How well kids make that shift to memory-based problem-solving is known to predict their ultimate math achievement.