0.o really? My teacher said I could use both BrE and AmE in my essays and yet every time I turn them in, she would add an additional "s" to the words "toward" I used.
Even though she's told you that you can use either BrE or AmE in your essays, it may be that she (for some reason) believes that "towards" is the only acceptable version. Is it possible that the rest of your essay sticks to BrE but then you suddenly throw in an AmE spelling? Most teachers will tell their students that they can use either BrE or AmE but encourage them to stick to one or the other throughout any one essay. A mix of the two can get very confusing.
I've been thinking about this on and off for the last hour. After trying out dozens of sentences, I am no longer sure what I say, but I think I might say:There's a silent b at the end of 'lamb'. I think 'on' is acceptable. Stick an extra tonto the end of 'set' if you are writing about a badger's home. I think I'd accept 'at', or just 'on'. If you use the word "untoward", don't add an "s" at the end of the word. I'd accept 'to' and 'on to', but not just 'on'.
I know, I know. There is no logic there - and I might give a different response tomorrow.