Determine which students already sing in a tenor range, or who will be singing tenor in the future. Prior to any voice change, teach your male students to use their "head voice" and project their singing through their sinus cavities, which will help them to project higher and farther.
Change your students' training regimen to concentrate on singing from their "chest range" after their voices have changed. Include diaphragmatic and breathing exercises and instruct them to breathe into their diaphragms only. Make sure they don't expel air from their lungs when singing, as this will not enable them to sing in proper form. Include instruction on how to properly form their mouths and tongues as they are singing.
Teach your students, male and female, to use correct vocal techniques for their voices. Remind them to sing in their own register (if they try to sing too high (soprano) or too low (baritone or bass), they run the risk of developing polyps on their vocal cords. If you do find a song which contains notes which are just a little high for your tenor students, work carefully with them in reaching these notes. Help them to use "head voice" for these notes. S
Use your piano or keyboard during voice lessons, including technical and breathing exercises. Have your students sing the notes which you play on the piano. One way of introducing and using good technique is to have the students sing phonetic sounds and vowels as they breathe and exercise their vocal cords and diaphragms, example, "em-en-em-en-em" or "la-la-la-la", "lo-lo-lo-lo", le-le-le-le" and "lu-lu-lu-lu".
Remind your students to drink plenty of room temperature water during the day, particularly before and during voice lessons. If students develop respiratory illnesses, encourage them to drink hot tea daily while they're sick. If students try to sing without drinking water, they will find it very difficult since their throats and larynxes are dry. Breathing air down into the diaphragm makes this dryness worse.