Everyone (here and there) pretty much agrees that studying culture and idioms is a good thing. The question of "how much" and "which ones" still remains. I would add "how" and "when" to the list.
A few points to think about:
- Language by its very nature is idiomatic & often figurative (not literal) - all languages, not just English
- Can you recognize and identify idioms and idiomatics structures in your own language?
- What are some of them?
- How do they relate to culture? (eg come from sports, pastimes, popular culture, etc)
- How are they like or different from English idioms?
- Are there any idioms or expressions in your own language that are the same or almost the same as in English?
- How would you translate into English or explain ones that are different, e.g. don't use the same cultural images?
Earlier on the ESL teaching list, an instructor made a good point about not teaching idioms since their frequency can be very low. The ones about gambling do not show high usage frequency, at least not on UK lists. No doubt many other idioms known to native speakers are also low frequency. This brings up the question of what exactly cultural competency consists of.
In the original posting with all the gambling expressions, the writer mentioned certain gambling idioms only to show that they are part of a speaker's cultural competency. This does not mean that every student needs to learn gambling idioms. However, the teacher could mention it when idioms come from gaming. Likewise, a term such as "touch bases" might be explained as deriving from baseball, without going into details about the rules of baseball. Quite a few idioms in American English come from baseball and are applied to everyday and workplace situations that have nothing to do with baseball.
Anyone who has played the game Bingo will, of course, know where the expression "Bingo! comes from when it is used to indicate success or a winner. Whether or not a teacher should go into detail to explain the origin of such terms is, at best, a moot point, but they are unquestionable part of a speaker's cultural competency no matter how they are taught or learned.
Some years ago, Kenneth Croft, a San Francisco State University professor, developed a test to judge students' ability to compete certain culturally-bound expressions, e. g., "red, white, and ______," "a penny for your _______," etc. Croft's contention then was that the ability to complete a series of such expressions was indicative -- or at least related to -- cultural competence. Perhaps an updated test would be useful today. (Sutherland, US State Dept)
Comments have been made on teaching idioms. Idioms are of utmost necessity in using and understanding English. When you ask a student to "look up" a work in a dictionary you are using an idiom. It would be a bit frustrating to see your class staring at the ceiling. Also, as a student learns idioms, they become more confident about inferring meaning. My students wrote reflections
papers on ways they have learned English. One student wrote that when I said "Let's pick up where we left off yesterday" she realized pick up meant begin/ return and left off meant stopped because I referrred to the page numbers of the book. In the eight word sentence four words made up two idioms. (Flierl, Williamsville NY)
As Wayne Hall wrote, idioms have a wider range than the set of "colourful expressions" often quoted. The metaphoric use of "see" in "I don't see what you mean." is idiomatic. So is the use of "do" by the casual dresser who says "I don't do suits". Such idioms are all around us and include the going to future with it's use of a spacial verb to refer to time. These idioms need to be taught.
Correspondents have also mentioned business idioms that use sporting metaphors. It may help if the student knows the background to the metaphor but it isn't essential. Many UK businessmen use expressions like "making it to first base" or "take a raincheck" without even thinking of the US sporting origin of the idiom. Even more common in business English is the idiomatic use of war and battlefield terms in business. "Boeing is winning out over Airbus but Airbus is fighting back" "Pepsi has enlisted the aid of a new PR company". These idiomatic usages are less obviously idioms than the more colourful idioms that take a metaphor and use it as illustration like the high profile low usage "raining cats and dogs" but I think they are very useful to learners, especially those who need English for business.
Lakoff and Johnson, Metaphors We Live By, shows how our use of metaphors is far more widespread than we may have realised (good is up, seeing is touching, eyes are limbs, life is a container etc.) and it is often the experiential and cultural base of metaphors that slide into idiom, for idioms are nearly always closely connected with metaphor. I don't see a need to teach idioms as such but learners definitely need exposure to some of the concepts behind idioms they are exposed to. Chinese learners, for example, rarely realise that "see" can be used in a sense other than the literal one. Showing the metaphoric link between vision and cognition can give an insight and is useful later in idioms such as "It's perfectly clear that ...", "That was a brilliant idea" and "give an insight". (Tibbets, teaching in China)
Visual reminders can go a long way to help students understand and use idioms. I gave an assignment where I had students work in partners. I had idioms written on slips of paper, and the students drew one. One partner wrote the idiom on a sentence strip, and the other partner drew a picture on a large sheet of paper. There were very cute representations of such idioms as: button your lip, on top of the world, like a chicken with your head cut off, etc. We posted as many of these as our bulletin boards would hold. If you had the materials, perhaps older students could do the same thing with overhead sheets -- one student or set of partners assigned to prepare and present one idiom per class period, for example?
There's a cute poster of a number of idioms illustrated at this website -- the top poster -- back to school with idioms: http://www.teachertools.org/bulletinboards_dynam.asp#eoy
I'm sure you're all familiar with this website for ideas for idioms: http://www.eslcafe.com/idioms/id-list.html (Pfeifer, Arizona, USA)