When doing choral practice for pronunciation, have the students repeat it WITH the teacher. First “Listen” then “SAY IT WITH ME.” NOT: First “Listen” then “Repeat”. This gives the students further exposure to the correct pronunciation. It also allows them to follow your lip movements.
When I do this I say it with them once at normal volume. Then I say it again with the student, but I lower my voice and exaggerate my lip movements. They can still hear my voice, but now I can hear their pronunciation better. Also, when I make my lip movements bigger, they imitate what I do and so their pronunciation becomes clearer and they build helpful muscle memory.