A diphthong is a vowel sound that glides from one position in the mouth to another inside a single syllable, unlike a plain long or short vowel. Oi and oy both spell the same gliding sound heard in coin and boy; ou and ow both spell a different gliding sound heard in cloud and brown. Because oi/oy and ou/ow are two separate sound families, this worksheet covers all four spellings together, so your child can see how they group into pairs rather than treating each letter combination as unrelated. A common mix-up is placement: oi and ou usually appear inside a word, while oy and ow usually appear at the end, similar to the ai/ay pattern your child has already practiced, though there are exceptions worth noticing, like the ow in brown or crown, which is not at the end of the word.
This page asks your child to spot each gliding sound among words with a clearly different sound, complete a partly hidden word with the correct spelling, name which spelling is inside a whole word, and choose the correct word to finish a short, true sentence. Encourage your child to feel their mouth move while saying each word, since that glide is what makes a diphthong different from a steady vowel sound.
What your child will learn
Hear the oi/oy and ou/ow gliding sounds
Tell the two diphthong sound families apart
Match each word to its correct spelling
Choose a diphthong word that fits a sentence
Worked example
Coin and boy share the same gliding sound, spelled oi inside the word and oy at the end. Cloud and brown share a different gliding sound, spelled ou inside the word and ow at the end.
Common mistake
Mixing up the oi/oy sound family with the ou/ow sound family, since both are gliding diphthongs rather than steady vowel sounds.
Helpful hint
Say the word slowly and feel your mouth glide from one vowel position to another.
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