Yearbook or directory pictures differ from normal pictures in that they are normally taken in a more studio setting, with controlled lighting and uniform method that makes each picture, more or less, similar. But studio lighting is tricky, not everyone can use it effectively. These are some examples of my mobile studio work with students.
Pricing Structure#1: $25/head (minimum 5)
Pricing Structure #2: $25/head (no up-front costs, parents/guardians buy photos afterward)
Pricing Structure #3: $350 (up to 50 students)