No set rule governs how fast or how slow to introduce letter-sound relationships. One obvious and important factor to consider in determining the rate of introduction is the performance of the group of students with whom the instruction is to be used. Furthermore, there is no agreed upon order in which to introduce the letter-sound relationships. It is generally agreed, however, that the earliest relationships introduced should be those that enable children to begin reading words as soon as possible. That is, the relationships chosen should he high utility. For example, the spellings m, a, t, s, p, and h are high utility, but the spellings x as in box, gh, as in through, ey as in they, and a as in want are of lower utility.
It is also a good idea to begin instruction in sound-letter relationships by choosing consonants such as f, m, n, r, and s, whose sounds can be pronounced in isolation with the least distortion. Stop sounds at the beginning or middle of words are harder for children to blend than are continuous sounds.
Instruction should also separate the introduction of sounds for letters that are auditorily confusing, such as /b/ and /v/ or /i/ and /e/, or visually confusing, such as b and d or p and g.
Instruction might start by introducing two or more single consonants and one or two short vowel sounds. It can then add more single consonants and more short vowel sounds, with perhaps one long vowel sound. It might next add consonant blends, followed by digraphs (for example, th, sh, ch), which permits children to read common words such as this, she, and chair. Introducing single consonants and consonant blends or clusters should be introduced in separate lessons to oid confusion.
The point is that the order of introduction should be logical and consistent with the rate at which children can learn. Furthermore, the sound-letter relationships chosen for early introduction should permit children to work with words as soon as possible.
Many teachers use a combination of instructional methods rather than just one. Research suggests that explicit, teacher-directed instruction is more effective in teaching the alphabetic principle than is less-explicit and less-direct instruction.