Assess the student's voice to determine if he is capable of singing tenor. Your student may possess the other male vocal part, a baritone. In that case, you will not be able to teach him to sing tenor because he will have a bass-toned voice.
Determine what vocal the voice is by using a keyboard to play the notes from the "C" below "Middle C" to the "C" above "Middle C," which is the vocal range of a tenor. Instruct your student to try to match his voice to the tone. He probably will not hit all the notes, especially the high ones, if he is not trained. However, he should harmonize with the majority of them.
Teach the student to read music notes and recognize them on the keyboard. It is not necessary that he knows how to play the keyboard. He just needs to recognize a note when it is played and be able to read sheet music to determine what key to sing in.
Have the student complete a series of vocal warm-up exercises before each singing lesson. Hit each key on the keyboard within the tenor range one at time, beginning with the low octaves, and have your student harmonize his voice with each note.
Hit random notes on the keyboard, within the tenor range, and have your student match his voice to them. Hit a low note, then a high note to teach your student how to jump octaves and exercise strength and control on his voice.