Like most people, English teachers can find it tedious to address the same basic grammar points and vocabulary items week after week. It's repetitive and hardly sexy. What many teachers really want is to get into the subtle points of language, the nuances of sophisticated use. Teaching idioms and collocations can help us feel like we're giving our students some value for their money, something they might not be able to get in a standard dictionary. But this is a rather selfish way to go about teaching a language.
As we saw the other day, learning a language is a long slow process. The fact is that few learners move beyond the rudimentary levels. Most students arrive in my classes not knowing the most common 2,000 words of English.
Paul Nation has argued that the top 2,000 to 3,000 word families should be considered high-frequency vocabulary. For one thing, there is broad agreement from one list to the next as to what these words are. This gives us confidence that they are not merely an artifact of a particular corpus construction. This list of words will also give enough coverage that learners will be able to begin to function independently. Furthermore, the additional coverage gained by learning words beyond this level is minuscule. The next 1,000 words only increases your coverage by about 2% and the payback is smaller and smaller as you go up. That is not to say that students should stop at 2,000 words, but merely that it is at this level that they should really take over from the teachers. Finally, from a pragmatic viewpoint, 2,000 to 3,000 words is about all that one can realistically expect to deal with in a course of study, be it the six years of jr. & sr. high school language instruction that is common around the world or a one-year intensive English language program.
If you look at how common these words are, you find that the lower frequency words occur roughly 30 times per million words. So teaching anything less common (and idioms are almost always far less common) really requires some extraordinary justification.
I don't know any teacher who would address say the subjunctive before teaching the progressive aspect, yet when it comes to idioms and vocabulary, a different standard seems to be applied. Perhaps the problem is that teachers have very little sense of what 30 times per million words or 0.3 times per million words tells them. More on this to follow.
In this series: Idioms, Differences between the corpora, & Interpreting the frequencies