The next step is to work with the pharyngeal vowel exercise that I designed years ago. I have found it works with approximately 95% of singers. Have the singer sing a 5-tone descending scale with the tongue between the lips imaging the vowel space straight back behind the tongue. Then have the singer place the tongue inside the mouth and sing the five basic vowels in any sequence KEEPING the pharyngeal vowel space behind the tongue root. You will find a large, resonant, yet body-connected sound results. Vocalizing with the tongue between the lips in the middle register demands a body connection and this is a good way for teachers to vocalize any student who has difficulty with this concept.