Can you date your high school teacher after you graduate?
Tl;Dr: I did.
For those who want the whole story - feel free to read on!
It was Friday afternoon, 6th September 2013; 12 days until I turned 17. I arrived early to my first physics class of the year, excited to meet my new teacher. We had heard little about him before then, so I was curious despite my social anxiety.
No-one else was in the room, just this young teacher and myself. He had just passed teacher training, 23 years old, and - frankly - a bundle of energy. Mr Mason. He guessed my name from the register (then again I was 1 of 4 girls in a class of 14 people) and said how much he liked it. I wore a Ramones hoodie and bag, on which he commented. More people arrived, and there was a lesson on SI units.
He also taught us on Wednesday mornings. He gave us an exam on my birthday, and promised me an extra 0.49 marks when I jokingly complained.
Each Friday, I stuck around to talk to him after class about movies, tv shows, music, games - anything. I once pretended to not understand something in order to get help, not that I needed to. I had made an unlikely friend. Or, at least I thought it was unlikely.
My other friends noticed instantly. The lighthearted mocking became ceaseless. Friday lunchtimes were the worst, being immediately before class, where my friends would make remarks when I touched up my make-up and leave early for class...
It got to Easter, just before the break, when he and I were talking as normal; he told me he had applied for a job 310 miles away. "Oh" was all I could say. I left for home sooner than normal that day, and cried for most of my 20 minute walk.
He gave out his number to the entire class as a general revision aid. I used it - stupid photons having momentum but no mass! - and we spoke almost everyday from then on. Even after he left.
You can, but it is a tricky thing to do. It is certainly unprofessional in many instances. There is, often rightfully, a stigma attached to it.
In an event where you have an older man (say 40–50) dating an 18-year-old woman, there will be sideways glances, comments, etc. This is more likely to be true when the man in question is a teacher. There is a double standard when genders are reversed, but it is still stigmatized.
I would imagine that if a brand new teacher (say... 22 years old) dates an 18-year-old, there is much less of a stigma. Still, there is some.
There is likely a point where this drops off, but that point stems more from the age of the former student. If a 30-year-old former student dates a 40-year old teacher, I don't think anyone would say much about it. This is likely because their former relationship is less obvious or because that relationship may have undergone a change. The pair is seen more as equals.
I think that really does get to the core of the matter. A student and teacher have a relationship. In our society, that relationship is hierarchical with the teacher in a position of responsibility and power. We have an innate (and well-founded) fear of abuse of power. The less a relationship between student and teacher resembles what it did while they were in the classroom, the more likely it is to be accepted.
You can do a lot more than that.
My high school music teacher had a student that was particularly bright. After she graduated, she moved to the big city for a few years before coming back to the smaller city where she grew up. She reconnected with her old music teacher, and about ten years after she had graduated, they got married. They now have four children and from the odd time she pops up in my social media feed it seems like things are going well for them. I imagine they must have gotten a lot of jokes about it over the years, and he is probably about 15 years older than her, but they've built a life together now.
Of course, there was that time in between for her to grow up and become her own person. So I'd say that anyone with a crush on their high school teacher should probably go through a similar process first ;)
In the United States it is considered taboo for a teacher to date their students even after the student graduates. This is for number of reasons, but mostly because of expectations carried over from time in school.
Teachers are expected to not think about their students sexually, and for good reason.
Almost all high school students are under the age of consent (typically 18 in the US but there are exceptions for people who are close in age). This makes any behavior that could be interpreted as sexual, a predatory behavior. Teachers can and do lose their jobs over this, and less. I know a number of teachers who have a strict, no physical contact rule, to protect them against the perceived risk. This means no hugs, or pats on the back.
Teachers are in schools to teach. Even if the student is legally an adult, sexual behavior is unprofessional. These relationships are counter to the teachers job and will likely get a teacher fired. A teacher is in a position of power, and may show favoritism to a student with whom they are in a relationship. If there is a breakup, it's even worse. Forget students, teachers are discouraged from dating other teachers they work with closely because if it doesn't work out, the working environment is destroyed.
So why don't teachers date students immediately after the students graduate? Because teachers aren't supposed to have had any relations with students before they graduate. It's like in old times finding out someone getting married is pregnant.
A few years out of high school it's no big deal. However, many teachers have trouble getting away from the mentality they were ingrained with: no relations with students. They can't help but see the ex student as a student and they are affected by the taboo.
So yes... You can date your teacher, however, they likely won't be interested until a few years after graduation.
If the former student is 18 and is no longer in any way associated with the school, and is not special needs, then the former student is not creating any problems for herself (himself). The teacher, however, is likely to be put under a microscope. If the teacher doesn't have tenure, don't expect to be rehired - and stuff like that can be a continuing problem in the job market. If the teacher has any past questionable activities of any kind administration will make an assumption that he has done something wrong. At one time this didn't raise many eyebrows, but today it can be career and personal suicide.
Most teachers create a personal mental barrier to avoid seeing young people as potential partners. You cannot do your job if you allow yourself to see students as dating material. If you cannot separate the young people from peers then you probably ought not go into teaching. That's my humble opinion.
(But look at the President of France. He's doing OK. But that is not the USA.)