Diphthongs are higher level phonics skills that students often struggle with. You can teach diphthongs in a straightforward way by following these tips.
First, make sure students have the correct understanding of diphthongs. At this point, your students should have heard of digraphs in their phonics lessons, and should remember that they are composed of two letters together that make one sound. Explain to them that some letters make a more complicated sound together, and that you have to move your mouth around to make the sound. Write the letters "oy" on the board. Pronounce the sound that they make, emphasizing how your mouth moves around to make the sound. Teach each diphthong individually or in pairs (e.g., "oy" and "oi"), leaving plenty of time for practicing each diphthong before moving on to another. By the end of the diphthong unit, you should have covered the following diphthongs: oy, oi, oo, ou, ow, aw, au, ew.
To make the instruction a bit more interactive and helpful for students of all modalities, try incorporating some of these activities.
Whole Class - Brainstorming Lists
Each time that you teach a new diphthong or pair of diphthongs, add a column or two to a large "Diphthong Chart" that you should have hanging on the wall. Then encourage your students to come up with a list of words that contain the new diphthong(s). For example, they might come up with the words toy, boy, soy, loyal, and royal for the "oy" diphthong, and they might come up with boil, foil, soil, coin, and noise for the "oi" diphthong. If you'd like, you can write these words on note-cards and Velcro the note-cards onto the chart instead of just writing them in. This will allow for plenty of practice later, where students can take turns sorting the diphthong words into the appropriate column. This can even be an activity included in a literacy learning center for several weeks after diphthong instruction. If students have difficulty thinking of words that use that diphthong, they can use a modified version of the Fry list for some ideas.
Practice in Pairs
Divide students into pairs, and instruct each student to make up to three sentences with the diphthongs on the list. For example, they might write "The boy had a toy" or "I set soil on the foil." After they have written three sentences, encourage them to pair up and read each other's sentences. The advantage of this practice activity is twofold. It not only gives students practice in reading the diphthongs, but it also enables them to write the diphthongs and to check each other's work. Remind students to correct their partner's sentences gently, and explain that taking corrections is part of becoming a good writer. This will minimize the hard feelings that students may feel during the correction process and enable them to feel like a team with their partners.
You can also give students more practice in reading diphthongs or in other aspects of phonics by using some phonics activities or reading games for review.
Circulate during the paired practice session, and listen to how students are sounding out diphthongs. If students need more help, give additional instruction on the specific diphthongs that seem to be throwing them off. These activities have been successful if students are able to sound out most diphthongs most of the time.