The International Phonetic Association (IPA) which devised a method to categorize spoken sounds, says American English has 44 sounds—20 vowel sounds and 24 consonant (and digraph) sounds. The IPA has devised symbols for each of these sounds—most of them letters of the Latin alphabet with some Greek letters and other symbols thrown in. Speech pathologists use these symbols to write down the exact sounds a student speaks when they are identifying speech problems.
In general, American English has fewer sounds than British English. Standard English (usually considered the way English is spoken by someone from the Midwest) has 16 vowel sounds, at least four fewer vowel sounds than standard British English. Since accents vary from region to region, some parts of the US might have more or fewer vowel sounds.
When a child is learning to read in English, making a sound is not the problem; it is the many ways a single sound can be shown in letters.
Some teachers have tried to help students, especially ESL students, to master the sounds by adding symbols to letters with multiple sounds: a curve over a short vowel, a horizontal line over a long vowel, and printing two letters that have a single sound as one letter without a space between them. This does make it easier for the student to associate sounds with symbols, but teachers have found the students grow dependent on the symbols and cannot shift to reading letters without those symbols.
Because students have so much trouble matching a sound to a letter, many reading methods have developed. However, a study by the U.S. government a few years ago found that a systematic phonetic approach works best with young children learning to read.