They generally don't have the same meaning.
As for sth. changes the focus of the conversation. It is almost always used to draw a contrast; it can often be thought of as an equivalent of however.
My brother loves blueberry pie. As for me, I think it's disgusting.
Here, as for me can be neatly replaced by however.
My brother loves blueberry pie. However, I think it's disgusting.
When being used only to change focus and not to draw a contrast, as for sth. can be an equivalent to regarding.
I really must do some laundry. And as for these dirty dishes, I don't know when I'll have time to wash them.
So here it merely changes focus. However wouldn't work here because both the laundry and the dishes must be cleaned, not one or the other.
I really must do some laundry. And regarding these dirty dishes, I don't know when I'll have time to clean them.
(The last sentence isn't entirely natural speech, but the meaning is clear.)
As to in your example means in order to.
You must arrive early as to see Henry before he leaves for the airport.
As to is formal, almost pretentious in everyday speech, but commonly used in the workplace.
Sometimes it's said as so as to, which is even more formal and pretentious, except in the workplace. And even then, it can sound a little pretentious.
You must arrive early so as to see Henry before he leaves for the airport.
"In order to" and "(so) as to" are too formal for everyday speech. The most common way to express this is so [someone] can, e.g. "so you can," "so I can," "so they can," etc.
You must arrive early so you can see Henry before he leaves for the airport.
And now for the exception. As to is occasionally used as a synonym for as for [regarding], but that is very formal, almost archaic, and almost always perceived as pretentious. A movie villain might say "as to":
As to your friends, we are quite safe from them here on this fully operational battle station.
Replacing as to with as for...
As for your friends, we are quite safe from them here on this fully operational battle station.
...and replacing as for with regarding
Regarding your friends, we are quite safe from them here on this fully operational battle station.
My advice? Forget about the exception, learn the difference between as for [however] and as for [regarding], and say so [someone] can instead of "(so) as to" or "in order to".
Those two mean the same thing: the deadline is Friday. There's a slight difference in tone, though.
The first wording (doesn't..until) has a more relaxed tone; it's almost suggesting that a little bit of procrastinating is okay. The second wording (has..by) suggests more of a sense of urgency.
So, let's say it's Tuesday, and I'm working on a report. A coworker asks me out to lunch. If I think I can go to lunch and still make my deadline, I might say:
Sure, let's go. This report doesn't need to be ready until Friday.
but if I think that going out to lunch now means staying late on Thursday, I might be more inclined to say:
No, sorry. This report needs to be ready by Friday. Maybe next week.
That said, this is a somewhat subtle nuance, and the two situations wouldn't necessarily require those respective wordings.
Similarly, let's say I'm the boss, and I'm assigning the report to a subordinate, who asks me, "When do you need this report?" If I answer:
The report doesn't need to be ready until Friday.
that implies I don't need it right away. I might say that on a Monday or Tuesday, but I wouldn't say that on Thursday. However, if I say:
The report has to be ready by Friday.
that implies a more urgent sense in the matter, and perhaps someone will be in hot water if the report is late.
Best Answer
I think at is your best choice; that's the preposition usually used in that context.
More specifically, I would use at, because we usually say at all levels:
It may be worth noting that, at least in the U.S. educational system, all of high school is considered one level, consisting of four grades. So, this is the way I'd recommend saying this (depending on what grades you taught):
However, that might be different in other countries.
One other thing worth mentioning: when we use a past tense verb with the phrase "in high school," that usually indicates an activity we did as a student.
So, I would avoid, "I had my student-teaching experience in Chattanooga High School" (even though it's not grammatically incorrect), because that could be interpreted to mean that you did student teaching while you were a high school student. It would be much better to say: