Initially, in the infancy phase, vocabulary growth requires no effort. Babies hear words and mimic them, eventually associating them with objects and actions. This is the listening vocabulary. The speaking vocabulary follows, as a child's thoughts become more reliant on its ability to express itself without gestures and mere sounds. Once the reading and writing vocabularies are attained – through questions and education – the anomalies and irregularities of language can be discovered.

In first grade, an advantaged student knows about twice as many words as a disadvantaged student. Generally, this gap does not tighten. This translates into a wide range of vocabulary size by age five or six, at which time an English-speaking child will know about 2,500–5,000 words. An average student learns some 3,000 words per year, or approximately eight words per day.

After leaving school, vocabulary growth plateaus. People may then expand their vocabularies by reading, playing word games, participating in vocabulary programs, etc.