When children learn to read using a phonics method, they start by learning that each sound has a one-to-one relationship with a letter. This makes reading seem logical to little children. See a B and say “b.” As teachers we don’t muddy beginning readers’ thinking by telling new readers that some letters mean more than one sound or that some letters, when paired with other letters, make totally different sounds or that some sounds can be represented by multiple groupings of letters. We save that for later, after children have “mastered” the concept of CVC words and blends.
But eventually children learn that written English is not as logical as it seems at first. Most advanced phonics instruction begins by teaching children consonant digraphs, two letters which, when paired, represent a sound that neither of the individual letters represents. The pairs which are taught first usually include ck, qu, sh, ch, and th.
If you find that children balk at learning this part of the “code,” this is normal. A four- or five-year-old’s understanding of logic is not the same as an adult’s. One-to-one relationships between sounds and letters makes sense to little children, but one-to-two relationships do not.
I recommend you start with one digraph per lesson. Just like beginning-of-word blends are easier for children to learn than end-of-word blends, beginning-of-word digraphs are too. The exception is “-ck.” I teach that while I am teaching CVC words containing blends.
But for other digraphs, I usually start with “sh” because there are lots of “sh” one syllable, short-vowel words such as shag, shed, shin, shot, and shut. I try to make learning “sh” at the beginning of words a game, using letter tiles and BINGO cards with “sh” words.
After a student becomes comfortable pronouncing “sh” at the beginning of words, I move on to another beginning-of-word digraph. The order isn’t important, but it is important that you constantly review the previously learned digraphs as you move along. For children who find remembering difficult, it is especially important to advance slowly, spending a large part of each lesson reviewing.
When the student is reasonably secure with pronouncing these digraphs at the beginnings of words, I might tackle teaching how to pronounce digraphs at the ends of words, one at a time. Or I might delay this kind of instruction, depending on how difficult it was for the student to learn the beginning of word digraphs.