As a teacher who OFTEN teaches while sick (strep, flu and other) I will say that there are several factors that contribute to my decision. First, though there are theoretically substitute teachers to sub in my class, it is frequently difficult to find one when I need one. Particularly because illnesses tend to creep up on us, it is sometimes too "last minte" to get a sub. Second, it is usually more difficult to create lessons and sub plans while I am ill than it is to come in and teach myself. Third, if I use up my sick days when I'm sick, what will I do when my 2 year old is sick and there's no one to take care of him? I agree that your child's teacher probably should have been at home recuperating from strep throat. In an ideal world, we could all stay home when ill, but in reality other factors interfere, sometimes rendering it not possible.