A diphthong is a vowel sound that begins with one sound and then glides into another within the same syllable. These special vowel teams make a single sound that is different from their usual short or long vowel sounds.
When vowels team up to make a new sound, think of them as “working together” to glide from one sound to another.
The diphthongs oi and oy make the /oi/ sound, like in coin or boy. The spelling oi usually appears in the middle of words, and oy usually comes at the end of words.
Remember: oi stays inside a word, while oy likes to play at the end!
The diphthongs ou and ow make the /ou/ sound, like in out or cow. They can sometimes make other sounds, but in first grade we focus on their most common /ou/ sound.
Think of the /ou/ sound as a surprised “ouch!”—both ou and ow can spell it.
Seeing diphthongs in sentences helps us learn how to read and understand them in real stories and passages.
When you read, listen for how the vowel sound changes or “glides.” That’s what makes it a diphthong!