Understanding Diphthongs
As students move beyond basic vowel patterns, they begin to encounter vowel sounds that don't stay in one position. Instead, the mouth begins in one position and glides into another as the sound is produced.
These are called diphthongs.
A diphthong is a vowel sound that starts in one position and changes or glides into another position within the same sound. The word diphthong can sound complicated, but the idea is actually pretty simple. Instead of holding one steady vowel sound, our mouth moves as we make the sound.
Some of the diphthong patterns students commonly encounter include:
oi and oy
coin, boil, point, toy, boy, enjoy
ou and ow
out, cloud, house, found, cow, brown, flower
There are also other vowel patterns that students encounter as they continue developing their decoding skills, including igh, which represents the long /ī/ sound in words such as night, light, and bright.
Why Teach Them Separately?
Although these patterns all fall into the broader category of vowel patterns, that doesn't mean they should all be introduced at the same time.
When teaching phonics, more is not always better.
Students need time to hear a new sound, connect that sound to its spelling pattern, practice reading words with the pattern, and then apply it when reading connected text.
For that reason, I would introduce oi and oy together, since they represent the same sound but typically occur in different positions in words.
Then, once students have had enough time to develop confidence with that pattern, move on to ou and ow.
Later, introduce igh.
Breaking the patterns into smaller pieces gives students an opportunity to truly learn each one instead of trying to memorize several new patterns at once.
Where Does the Sound Occur?
One activity I really like when teaching vowel patterns is having students sort words based on where the sound occurs in the word.
For example, with oi/oy, students might sort words into three categories:
BeginningMiddleEndoilcoinboyoysterboiltoy—pointenjoy
This helps students begin noticing something important about English spelling patterns.
Sometimes a particular spelling pattern is more common in certain positions within a word.
For example, oy is commonly found at the end of a word, as in boy, toy, and enjoy, while oi is commonly found in the beginning or middle of a word, as in oil, coin, and point.
We can do the same thing when we introduce ou/ow.
OU: out, cloud, house, found
OW: cow, brown, flower, owl
Have students listen for the sound, identify the pattern, and then decide whether they hear it at the beginning, middle, or end of the word.
Make It Multisensory
As with all phonics instruction, don't make the lesson simply about looking at a word and memorizing its spelling.
Have students:
Say it → Hear it → Build it → Write it → Read it
For example, say coin and have the student identify the sounds they hear. Then build the word with letter tiles, identify the oi pattern, write the word, and read it in a sentence.
You can also have students sort word cards into categories and explain why they placed each word where they did.
That conversation is important.
We aren't just asking, "What does this word say?"
We are helping students understand how the word works.
E3 Takeaway
Diphthongs may sound like a complicated phonics term, but the concept is something students can hear and feel.
The vowel sound begins in one position and glides into another.
As teachers and parents, our job is to make these patterns manageable. We don't need to introduce every diphthong at once. Instead, we can teach oi/oy, give students time to practice and apply it, then move to ou/ow, and eventually introduce other patterns such as igh.
Small steps, repeated practice, and opportunities to hear, see, say, build, write, and read the patterns can make a big difference.
Phonics instruction isn't about how quickly we can get through the patterns.
It's about making sure students have the foundation they need to become confident, independent readers.
From the Teacher’s Desk,
E3 Learners
Engage. Empower. Educate.
