I worked as an aide for three years and briefly as a sub. Even if the principal and teacher want to hire you there will still be paperwork with the district, an official application, your W2, TB test and background check. Your TB test may be already on file as a parent volunteer but like any other job, especially a job working with children, they're still going to need all of this. Maybe the teacher is naive about how aides are hired and I'm sure she's busy getting ready for school but I would want some kind of confirmation from the district that you are in fact, employed. Also here in CA subs don't need a teaching credential but they are required to have a Bachelors degree (any subject) and must pass the CBEST, a state mandated test for basic academic proficiency. It wasn't too difficult but it takes some time to prep for it and sign up. You should find out exactly what's required, and I'm sure this info is available on the district website. Or you can just go in person and speak to someone.