how they can improve their pronunciation. This probably happens because we often don't teach pronunciation directly like we teach other things such as grammar. International House has a good online course helping teachers learn about teaching pronunciation.
What do you tell them? Practice? Listen to native speakers? Watch TV? Those are all legit answers and can help students, but you're going to have to go a bit more in depth. Below you can find some ideas to help you out. You can also find specific websites dealing with pronunciation in the article sites for lesson plans.
Physically Show Them
Different languages cause you to manipulate your mouth differently. Showing students how their mouth has to form the sounds can help. You can also try using charts which can be found in some ESL and EFL books.
The phonetic alphabet may be tough to learn, but it's incredibly useful when trying to teach pronuncation. Learn it and use it. Your students will thank you. Too hard? Invent your own alphabet. You can use words that sound similar or rhyme to help your students as well.
Speak Naturally and Link Words
While you may need to speak slowly for beginners, don't speak like a robot. English speakers naturally run words together. You don't want your students to say, "What. Are. You. Going. To. Do?" You want them to say, "Whaddya gonna do?"
English has word stress and sentence stress. Syllables are stressed inside of words, not every syllable receives the same stress. For example, you say, "TAble", not "taBLE".
In addition, sentences can change meaning depending on which word you stress. For example, "Give ME the pen" means that you want the person to give you the pen and not to give it to someone else. "Give me the PEN" means that you want the pen, not the pencil.
Going along with stress and not being a robot is intonation. Our voice goes up and down in pitch when we speak English. For example, "I'm so happy" would have your voice start at a low pitch and go up. "That's too bad" would start high and go low. Here are some Tips on perfecting your pronunciation.
Voiced vs Voiceless
Voiced means your throat vibrates when you talk, for example, when you say the letter "g". Voiceless is when your throat doesn't vibrate, like in the letter "k". Your mouth and tongue are in the same position for "g" and "k", but the former is voiced. Have your students feel how their throat vibrates when they talk.
Aspirated vs Not Aspirated
This is when a little puff of air comes out of your mouth. For example, "b" is aspirated, but "p" isn't. Your students can hold their hand in front of their mouths and feel the air come out.
Words such as "15" and "50" are easily confused. 15 has a long vowel while 50 has a short vowel. I saw a teacher demonstrate this once with a rubber band. The students had to say the word and stretch the rubber band if it was a long vowel. Simple, but it works.
Make a worksheet with words that are nearly the same, such as "tip, tap" or "fashion, passion" or "pray, play" or "ship, sheep". They should say them aloud and can work in pairs, groups, or as a class. You can even use pictures or have them draw, such as "a sheep is on the ship". Ship or Sheep is a good website for these.
Have Some Fun
Have your students try to impersonate people. This is fun and a relaxed way to learn pronunciation. They can practice with different accents, such as British, Australian, Irish, etc. Have them take it a step further and imitate foreigners speaking their language.
Tongue twisters are another favourite among EFL learners, especially since it's hard for native speakers. Demonstrate a tongue twister and your students will see that making mistakes are ok and can be fun. There are a number of fun activities you can do with your students.
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