/fa/ - Fashion

I am 24 years old, and at the start of the next school year I will be in my first teaching position at a school. I currently have long hair - past my shoulder blades - and a fairly robust beard. I wear flannels, chunky sweaters, etc. and generally aspire to look sort of..cozy.

Anyway, the school district hasn't asked me to change - I'm really well qualified and they all absolutely loved me during the interview process. However, I'm going to be working with 10th graders as a writing teacher. I want these people to become close to me, because I want to make good writers out of them after experiencing how terrible people out of HS are at it in my college years.

What advice does /fa/ have to pull off "nice teacher" as a 24 year old without going too far towards looking like a dad or like a preppy tryhard?

As far as my facial hair/long hair I think I'm going to go for medium length hair and shave down to a very short beard. I have good coverage and my beard is pretty thick and neat even when it's shaved down to an inch or less. Is that good? Should I go clean?

To reiterate, this is more about appealing to/not intimidating the 15-17 year olds I will be dealing with than looking strictly professional.