E.T.
As a teacher, I would not use them in the classroom. Partly that is because I don't like scents of any kind. Partly that is because I have a co-worker who has a severe allergy to scents that can set off an asthma attack. I have another co-worker who has severe migraines that can be sparked by scents. We have a couple of students with cystic fibrosis who have severe breathing problems. We have some students on the autism spectrum who have sensory issues and are very sensetive to smells. We have a student going through chemo who is very sensitive to smells.
I sometimes go into a school social worker's office. It is a very small office. She has a diffuser with vanilla scent in it. I can't stand to be in her office for more than a couple of minutes before the scent becomes overpowering and almost makes me sick to my stomach.
Essential oils should not be in the classroom in my experience.