It brings more contrast to the sentence.
It is kinda possible without it, however the meaning will shift:
Если она будет подлизываться к учителю, её оценки от этого не улучшатся, а другие дети от неё отвернутся.
It immediately sounds like "her grades won't be any better, and other children will turn their backs on her". Grammatical, surely, but introduces the idea of similarity, that is, you are just listing the consequences of her actions. Why does it happen?
- It happens because "а" doesn't only introduce contrast of things you talk about. It is more complicated than that: sometimes it intorduces the subjective narrative contrast: "you might have expected me to end the sentence — yet, I have got another thing to add".
- sometimes "а" introduces another subject: "The girls like juice, and
the boys only drink water and beer" would use "а". It is also used
to push narrative forward when there is a link between parts. Then it
loses its contrasting meaning: _"The girls like juice, and juice is
good for your health" ~ "Девочки любят сок, а сок полезен для
So "а вот" is essential here to signal that you — unambiguously — want to show a contrast here: "first, she won't achieve anything useful — however, she is totally going to get herself frowned upon by other kids".
- the structure with "а вот" is "She won't succeed in A, yet what she will succeed
in is B".
- when just "а" is used, it is less effective and can be also interpreted as "What will happen is A and B".