A diphthong is a vowel sound that starts in one position and glides to another within the same syllable. Your mouth actually moves while you say it. English has 8 diphthongs, but phonics programs typically focus on the 4 most common spelling patterns: oi, oy, ou, ow.Here’s the full breakdown with word lists and teaching notes.
What makes diphthongs different
Long vowels hold a single steady sound. Diphthongs glide: coin starts at /ɔ/ and glides to /ɪ/; outstarts at /a/ and glides to /ʊ/. Kids who’ve learned to listen for steady vowel sounds sometimes miss the second part of a diphthong — or hear it as two separate sounds and try to spell it phonetically (“oi” → “oy” in a word ending).
OI — /ɔɪ/ in the middle of a word
The spelling oi appears in the middle of a syllable.
Word list: boil, broil, coil, coin, foil, join, loin, moist, noise, oil, point, poise, poison, soil, spoil, toil, void, voice, choice, avoid, appoint, anoint, exploit, ointment, adjoin.
OY — /ɔɪ/ at the end of a word or syllable
Use oy when the /ɔɪ/ sound comes at the end of a word or before a vowel suffix.
Word list: boy, buoy, cloy, coy, decoy, deploy, destroy, enjoy, joy, loyal, oyster, ploy, royal, soy, toy, troy, annoy, employ, convoy, corduroy, flamboyant, gargoyle, joyful, voyage.
Rule of thumb: ends the word → oy (boy, joy, toy). Middle of word → oi (coin, boil, voice). This rule works about 90% of the time.
OU — /aʊ/ in the middle of a word
The spelling oumakes the /aʊ/ diphthong sound in the middle of a syllable. (Note: ou also spells other sounds in “you,” “could,” “soup” — teach those as separate patterns.)
/aʊ/ word list: bounce, cloud, count, couch, doubt, flour, found, foul, ground, house, loud, mount, mound, mouse, mouth, noun, our, out, ouch, pound, round, scout, shout, snout, sound, south, sprout, stout, trout, voucher, wound (as in wrapped).
OW — /aʊ/ at the end of a word
Use owfor /aʊ/ at the end of a word or before certain consonants (-n, -l). Note: ow also spells the long O sound in “snow, blow, flow” — a common confusion point.
/aʊ/ word list: bow (to bow), brown, brow, clown, cow, crowd, crown, dow, down, drown, fowl, gown, growl, howl, jowl, now, owl, plow, pow, prowl, row (to row a boat), scowl, sow (a pig), town, towel, vow, wow.
Disambiguation:“ow says /oʊ/ in snow and /aʊ/ in cow.” Teach both readings and have children try both when they see ow — context usually makes the right one obvious.
The other 4 diphthongs (less common in phonics programs)
- /ɪə/ — ear spellings: ear, hear, fear, near, clear, deer, beer, peer, here, mere, pier, tier.
- /ɛə/ — air spellings: air, bare, bear, care, chair, dare, fair, glare, hair, hare, pair, pear, rare, share, spare, stare, there, ware, wear.
- /ʊə/ — ure spellings: cure, lure, pure, sure, tour, your, poor, moor (varies by accent).
- /eɪ/ — treated as long A in most phonics programs: day, play, rain, cake (see long vowels).
When to teach diphthongs
Diphthongs come after long vowels (magic-e + common vowel teams) are secure — typically late Year 1 / mid-kindergarten in a well-paced program. The oi/oy and ou/ow pairs are the priority; the ear/air/ure patterns can follow in Year 2.
Common kid mistakes
- Spelling oi at the end of a word.“joy” → “joi.” Teach the position rule: end of word = oy.
- Confusing ow /oʊ/ and ow /aʊ/. Drill minimal pairs: blow/brow, low/cow, flow/fowl.
- Missing the glide.Reads “coin” as “con” or “coon.” Have them say the two parts slowly and join them.
The phoneme map includes audio for all diphthongs — use it so your child can hear the glide before practising in words.
The ear/air/ure patterns above are r-controlled vowels — part of the first-grade phonics skill set. If this stage is taking longer than expected, our guide to how long phonics actually takes covers what’s normal variation.