While kindergarten is meant to be a gentle, low-stress introduction to formal schooling, it’s a critically important milestone for little learners, who are developing at an astounding pace.

Corrected: An earlier version of this story incorrectly identified the tiers associated with challenging words. Children who enter kindergarten with a small vocabulary don’t get taught enough ...

Filling a child’s new backpack with a box of crayons and school supplies is part of the bittersweet ritual of preparing a kindergartener for the first day of school. What parents may not realize is ...