This debate really seems to be about two different things, spelling and pronunciation. The letter w (and y) is often used with other vowels (and sometimes alone as well) in spelling to
reperesent a vowel sound. In the words
hi and
by, the letter
i and the letter
y are representing the same sound. To add to the confusion, English has many diphthongs, or two-sound vowels. Two-sound vowels often begin or end in a sound very similar to a w sound or y sound. The easiest to here are
oy (boy) and
ow (cow), which can also be spelled
oi (coin) and
ou (house). So, it is very clear, that in
spelling, w and y are like vowels. Our educators have found it much easier to just tell our kids that those letters are vowels because they are so often part of a vowel sound's spelling, and because we so often hear sounds so similar to them when we speak due to diphthongs and sounds like the oo sound (in the word soon).
However, the one of the linguistic characteristics of vowel sounds (not spellings) is that a syllable will occur when we have a vowel sound. Some of these vowel sounds become very much reduced in the schwa sound, and so we barely say them, but they are still linguistically there. In this reagard, w and y are not vowels, because they do not cause us to add another syllable to a word. We can easily hear that w and y don't create syllables in words that begin with a w or y and are only one syllable long. For instance, the word "way", according to the a-e-i-o-u-and-sometimes-y-and-w rule, has 3 vowels, but it is only one syllable, so, according to the linguists, actually only has one vowel sound, and I doubt any linguist would consider the w or the y to be that sound.
All of these ambiguities are why linguists have created the catagory of "semi-vowel" just for the w sound and y sound. They acknowledge that these letters have some characteristics very similar to vowels, yet not enough to be considered a full-fedged vowel.
It makes sense to me that teachers choose to keep it simple and tell the kids what will make it easier for them to read and spell, no matter what the perfect linguistic categorization of that letter is. A five year old doesn't care that "cow" is spelled with a traditional vowel, and a w, yet is only one syllable long, and learning to read is hard enough that teachers certainly wouldn't bother telling these kids that w and y are semi-vowels. The teachers will do whatever they think makes it easiest to learn.
When I am teaching non-native English speaking adults, I tell them that w and y can represent vowel sounds, but that they are not truly vowels because my students are aware of, and often struggling with, syllables. So if I tell them that w and y are vowels, they will (and do) question why they do not cause the word to have more syllables. With kids learning to read in a native English speaking environment, it is a completely different learning situation.
All I ask of the confused parents out there is not to tell your kids something different than they are learning in school; it will make things very confusing for them.
That's my two cents' worth.
~Miss Mandy