In addition, it is not clear how many months or years a phonics program should continue. If phonics has been systematically taught in kindergarten and 1st grade, should it continue to be emphasized in 2nd grade and beyond? How long should single instruction sessions last? How much ground should be covered in a program? Specifically, how many letter-sound relations should be taught, and how many different ways of using these relations to read and write words should be practiced for the benefits of phonics to be maximized? These questions remain for future research.
Diphthongs are linguistic elements that fuse two adjacent vowel sounds. English has four common diphthongs. The commonly recognized diphthongs are /aʊ/ as in cow and /ɔɪ/ as in boil. Three of the long vowels are also in fact combinations of two vowel sounds, in other words diphthongs: /aɪ/ as in "I" or mine, /oʊ/ as in no, and /eɪ/ as in bay, which partly accounts for the reason they are considered "long".