I cannot make my students in the choir sing higher and on the correct pitches. I show them high with my hand to sing higher and they do not do it. Perhaps they can not sing higher but the problem I think is that they do not know how to make their voices higher. And again they have a very limited range and they speak more the notes rather than speaking them. Whatever register I give them seems wrong. In addition their voices are too soft and as a choir they do not sound loud and clear. What shall I do?