The typical first-grader would begin school with a vocabulary of around words.

The typical first-grader would begin school with a vocabulary of around 10.000 words.

Explanation:

When talking about a kid's vocabulary, most teachers and psychologists are referring to the group of words that a specific child knows. The amount of words each child knows grows over time, and school plays a big role in this development. At 5 years of age, a typical first-grader will start elementary school with around 10.000 words in his/her vocabulary. After one year of attending school, that same child would have learned from 2.000 up to 5.000 new words.