Teenagers Are Wordy Ungood.

Teenagers have been warned they are becoming unemployable because they use a vocabulary of just 800 words.

Sounds shocking and there are inevitably calls for "urgent action" to make them use more words. However the details aren't nearly as clear cut:

The majority of teenagers should have developed a broad vocabulary of 40,000 words by the time they reach 16.

Linguists have found, however, that although they may understand thousands of words, many choose to limit themselves to a much smaller range in regular conversation and on a daily basis could use as few as 800 terms.

So it isn't as if they only know 800 words, but they only use 800 different words on a daily basis which is a very different thing. I've probably used fewer than 800 words today yet it doesn't mean that I am unable to use more words if I so choose.