The results of our testing indicated that native speakers of English
increase their vocabulary size by around 1000 word families a year starting
roughly at the age of about three. So, a 13 year old learner typically has a
vocabulary size of around 10,500 word families and a 17 year old around
14,000 or 15,000 word families. Where English is taught as a foreign language,
I consider that learners should be aiming close to 1000 words a year in order to
reach the 8000 to 9000 words needed for unassisted reading of unsimplified
texts such as novels and newspapers.