ESL (English as a Second Language) students need to know slang and idioms to understand the real language that native English-speakers use. Even though some teachers fear that teaching slang will debase the language, "Street Spanish" author David Burke says not knowing slang and idioms will keep your students outside the English mainstream. (See Reference 1.) Give your students the tools they need to enter the real world of modern English communication by teaching them slang and idioms.
Present slang and idioms in a realistic context and in manageable chunks. Too many new expressions at once will overwhelm your students, especially those at the lower level. Burke suggests using realistic dialogues containing no more than a dozen new slang expressions or idioms. Break up longer dialogues from textbooks into smaller lessons. Have students guess the meanings of expressions before you explain them. (See Reference 1.)
Practice the conversations with realistic reductions, as linguists call the contracted forms native speakers use. For example, we often pronounce "What do you want?" as "Whaddaya want?" Use your voice or a natural-sounding recording to model the conversation. Then have students practice with partners. If they practice natural-sounding speech, they will later be able to understand native speakers who talk fast. (See Reference 1, Resource 2.)
Use games and performance activities to reinforce the new expressions and to make learning fun. For example, have students write and perform their own dialogues using the list of idioms just learnt. (See Reference 2.) Have each group of three or four students draw illustrations for a different idiom on a piece of poster paper to display in class. Choose expressions that make funny pictures, such as "He is biting off more than he can chew." Or write idioms on notecards to use for charades. Have one student at a time come to the front of the room to select a card and act out the idiom.
Add variety and interest by using authentic or real-life materials to introduce and reinforce slang and idioms in your ESL classroom. For example, use TV or movie clips on video, comic strips, print or TV advertisements and songs. Any medium that brings authentic language into the classroom will help your students master the colloquial English they hear every day in the world outside.
Burke says that you shouldn't equate slang with vulgarity or obscenity. (See Reference 1.) You can monitor the material you bring to class for appropriateness to the age level of your students.