and your teacher was full of shit, mate.
there is absolutely no foundation, historical or grammatical, to that belief.
‘And the idea that and must not begin a sentence, or even a paragraph, is an empty superstition.
The same goes for but.
Indeed either word can give unimprovably early warning of the sort of thing that is to follow.’
Kingsley Amis, The King’s English (1997)
‘Contrary to what your high school English teacher told you, there’s no reason not to begin a sentence with but or and;
in fact, these words often make a sentence more forceful and graceful.
They are almost always better than beginning with however or additionally.’
Professor Jack Lynch, Associate Professor of English, Rutgers University, New Jersey
‘There used to be an idea that it was inelegant to begin a sentence with and.
That idea is now as good as dead.
And to use and in this position may be a useful way of indicating that what you are about to say will reinforce what you have just said.’
Sir Ernest Gowers, The Complete Plain Words (1954)
‘There is a persistent belief that it is improper to begin a sentence with and, but this prohibition has been cheerfully ignored by standard authors from Anglo-Saxon times onwards.’
RW Burchfield, New Fowler’s Modern English Usage