ok.. this is what my singing tutor used to tell me...

Singing comes from the stomach.... not the nose, not the throat...

throat singing, is when people squash their throats, to produce a coarse, nasal sound... The vocal chords may be resticted...

Head voice is when the singing is clear as a bell....not nasal (this is what I understand it to be...)

Get them to practise the vocal exercises... they may sound daft, but it does work....

I do.... ka ka ka ka kaaaaaaa kar kooooo karrr and make sure the tongue is flat, not pressed to the back of the throat. on the same note, or up and down the octave... or mmeee me meeeee mooooh moesss

Dictation is also really important when singing, and helps the voice to come over clear, even if the singer has to over accentuate the word just a little..

Other importants, are that they breathe properly, from the diaphragm, and try not to heave their shoulders up. Singing depends on the way the lungs are used...

The head in effect acts as an amplifyer for the sound and if the sound is surpressed in the throat, then the singers voice will not project as well...

got the below from the Britanica Encyclo...

In its physical aspect, singing has a well-defined technique that depends on the use of the lungs, which act as an air supply, or bellows; on the larynx, which acts as a reed or vibrator; on the chest and head cavities, which have the function of an amplifier, as the tube in a wind instrument; and on the tongue, which together with the palate, teeth, and lips articulate and impose consonants and vowels on the amplified sound. Though these four mechanisms function independently, they are nevertheless coordinated in the establishment of a vocal technique and are made to interact upon one another.

hope that helps...

Ella

knackered now... remembering all my singing tutors words from years ago...