What are Diphthongs? How do I Teach Diphthongs to my Students?

Vowels are one of the first key concepts we teach early readers –  the “superstars of the alphabet” – a, e, i, o, u (and sometimes y). Little do our students know, as they continue to crack the code of reading, vowel sounds become a lot more complicated! Take for example, the concept of diphthongs. Throughout this blog post, we will dive into the concept of diphthongs and provide some low-prep ideas to support student learning of these unique vowel sounds. 

Diphthongs, Defined 

A diphthong (pronounced dif-thong) is a special kind of vowel sound that is formed when two vowels come together in a single syllable. A diphthong is not classified as long nor short, but rather, something else entirely. Each vowel sound is uniquely heard as one vowel sound glides into the next. Hence why vowel diphthongs are often referred to as “gliding sounds”. Although the two vowels are still working together to make one sound, the sounds glide from one vowel sound into the next. Take oi for example. Say /oi/ and take notice of what your mouth is doing to articulate this sound…it begins as an /o/ sound and swiftly glides into the /i/ sound. 

Quick tip: A mirror can be a useful (and fun) tool to help students take notice of how their mouth changes as they say these diphthong sounds. I purchased a class set of cheap compact mirrors for students to use during phonics instruction and they are SO worth it! 

Diphthong Generalizations 

Fortunately, there are some guiding rules that can help make these otherwise tricky sounds a little more manageable for students. 


  • Use oi at the beginning or middle of a word
  • Use oy at the end of a word


  • Use ou at the beginning or middle of a word 
  • Use ow at the end of a word
  • If an l, n, el, or er follows the /ou/ sound at the end of a word, use ow.


  • Use au at the beginning or middle of a word
  • Use aw at the end of a word
  • If an l, n, or k follows the /aw/ sound, use aw.

If you are looking for a no-prep visual resource to support student learning of these generalizations,click here to grab our Diphthongs Digital Slides Freebie

How do I teach diphthongs?

Since diphthongs tend to be challenging for some students, it is best to introduce one pair of diphthongs at a time. Be sure to draw attention to the fact that these are two graphemes (letter pairs) that are representing the same phoneme (sound). Typically, diphthongs are introduced after students have demonstrated mastery of long vowels. 

After a pair of diphthongs has been explicitly taught, the following activities are highly beneficial to give students the multiple practice opportunities they need to deepen their understanding of this new concept.

  • Word Sorts –  if you are looking for a no-prep, print and go resource for students to practice diphthongs, grab our comprehensive practice packet here.
  • Word Building – consider using magnetic letter tiles to provide a multisensory experience 
  • Decodable text – spend time delving into each page and encourage students to go on a “word hunt” to find the diphthongs and get practice decoding them before you read. This will help students get additional practice at the word level and experience more success when reading connected text. 
  • Fluency Grids – create a fluency word grid with diphthongs and have students practice reading across the rows daily during your week of instruction. You (and your students) will be amazed at how much more fluent they become by the end of the week! 

What are your tried and true tricks for teaching dipthongs?  Tell us in the comments!  And don’t forget to grab these free dipthong teaching slides perfect for online teaching! 

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