Factors affecting English vocabulary levels in foreign language speakers

The Test Your Vocabulary site has found a few factors that influence the size of a non-native speakers vocabulary.

Academic performance helps, up to doubling your vocabulary size. But that doesn't tell us what helps academic performance.

Classroom participation matters too, but it's not the top factor. It appears to give you up to a 50% boost in vocabulary.

Outside of class is the biggest difference. Students who do "lots" of things in English outside of class have more than twice the vocabulary of those who "don't do much."

Living abroad gets you to and beyond 10,000. Up to one year abroad brings the average student from around 7,000 to around 10,000 words. After that, every year abroad gives you around 850 more words, or around 2.35 per day. (Compare that to the average American adult who learns 0.85 per day.)