I agree with Stuart Skelton (see comment here) that undergraduates don't want to get involved in the really heavy repertoire. (That's not exactly what he said. I'm interpreting.) I have praised the Merola program here for emphasizing the lighter lyric operas in their training.
However, there are a couple of things that students can learn at any age and any voice classification.
Anyone can learn breath support. Undergraduates can learn to carry the breath across the phrase and keep the pressure low in the body. These lessons will be valuable no matter what happens to the voice later in life. Good breath support lets the natural sound of the voice come out.
Anyone can learn to produce a proper legato. Let me repeat that. EVERYONE can learn to produce a proper legato. Jeeze, you guys. What do you do in your lessons--and by you I mean all of you--no one gets off here--if the subject of how to produce a proper legato never comes up?
The elements of a good legato are...
- The vowels all resonate in a similar space. This involves keeping the teeth a similar distance apart, emphasizing the forward formant, thinking about how the vowels are produced at all.... I said this was going to be a tirade. I'm just trying to put out ideas. Don't do what I say. Make up your own method. Believe it or not, this all enhances diction rather than interfering with it.
- The singer learns to keep the energy of the phrase going across the change from one note to another and during the consonants. Think of singing as being like a musical saw. The notes and the words change but the tone keeps going. This will eventually eliminate leaking air.
Quit trying to make your students into something. Teach them breath support and legato and wait to hear what comes out. Teachers often screw up students' entire lives by thinking they should begin with classification. I recommend the Cecilia Bartoli method--put off classification until the student is over 40. (Now that she's in her 40's she finally admits that she's probably a high lyric mezzo.) The very young should sing as much variety as possible. For the young classification is just choosing what they sound best singing.
I am speaking as a person whose classification was screwed up. I was actually told never to sing Mozart. How insane is that?