Take, for example, age 24 months. This data says that the average child—that’s the 50th percentile line—at 24 months has about 300 words. A child at the 10th percentile—so, near the bottom of the distribution—has only about 75 words. On the other end, a child at the 90th percentile has close to 550 words. For younger children, these surveys and data focus on
