Coursebooks are big on schwa. Is it because schwa is said to be the most frequent sound in the English language? Is it because it’s an “issue” for all students, no matter what their L1? Whatever the reason, students get a lot of exposure to it, and sooner or later, someone is bound to ask something to the effect, “How exactly is it pronounced?”
Cue the teacher making little grunting noises and talking about how relaxed the mouth must be to make this sound. At this point, we are on thin ice. When a student asks how schwa differs from the the vowel in duck, the thin ice cracks. Because no matter how clearly the teacher demonstrates his/her version of the two phonemes, the difference seems to be barely perceivable to the student.
Student thinking, “Surely such a small difference can’t be so important!”
Teacher thinking, “Aargh, get me out of here!”
Books sometimes present schwa as if it were just another phoneme, equivalent to any other. Phonemic charts may encourage this perception, with the occupants of each little cell seemingly equivalent to one another, like chocolates in a chocolate box*. The chocolates are all the same kind of thing, but just with slightly contrasting flavours. The schwa however is not the same kind of thing – instead of contrasting with other vowel phonemes, it may substitute for them in unstressed syllables. It’s precise sound quality is not its essential feature. When teaching it, we should focus on it’s role in differentiating stressed and unstressed syllables rather than its exact sound quality.
Attempting to demonstrate and drill the schwa sound is what takes us on to the thin ice mentioned above, because it is not sufficiently different from some other vowel sounds – the duck vowel in particular. Ironically, the distinction becomes even less clear the more we focus on it: all that attention causes us to place stress on the sound, which is precisely what it shouldn’t have. So to sum up: Don’t sweat the schwa!
* This is the reason why, in the PronPack Sound Chart, the schwa is given an exceptional position, to discourage the impression of equivalence with the other phonemes.