Sketching people can be stressful. Sometimes you can't get a recognizable likeness from a photo or even a life drawing. That's where sketching from yearbooks comes in. I "discovered" them when mixed media artist Laure Janus of Little Joys Studio showed us her art journals in which she had cleverly incorporated photos from high school and college yearbooks. Fascinated, I amassed a small collection of yearbooks dating from the 1919 through the 1960s, purchased from local flea markets. You can find them for as little as $5 each, and they're an interesting study of students from the past -- their aspirations, their interests. Many of them are no longer with us, but you wonder about their lives.
While you're wondering, you can sketch them. No pressure. No one will know if the student doesn't look exactly like his or her photo. You'll find that looking at rows and rows of student photos can help to isolate facial characteristics so that each drawing gets just a little easier.