Read along to practice your English and to learn the English phrases TO SIT IN ON and TO SIT OUTIn this English lesson, I wanted to help you learn the English phrase to sit in on. It's a nice phrasal verb with two prepositions at the end, which makes it a little confusing. This means to go to something like a class to observe rather than take it. At work, sometimes the principal needs to check if I'm teaching properly and so the principal will sit in on one of my classes. When you visit a sch...