Many people know that a phoneme is the smallest unit of sound that changes the meaning of a word .
But they are having more difficulty teaching children to identify and spell the 44 phonemes. 20 vowel phonemes. To produce a diphthong we have to make a change in pronunciation. Diphthongs still count as one phoneme but they are constructed from two vowel qualities, the first being longer in duration than the second. This is based on the work done at the University College London about a hundred years ago, when phonetics was quite a young academic discipline.