Shelflife
I remember in primary school the teacher saying " we never use the word 'got' its an ugly word. We also learned that when writing to never begin a sentence with the word ' And' .
You are right that Primary School teachers did tell children not to start sentences with, as I remember it, "and, but or because" but this is not a rule if grammar but a rule if thumb, generally to stop overuse of these words. The "adult" rules are:
You may begin a sentence with and or but when it improves clarity or emphasis.
You may begin a sentence with because as long as the sentence includes an independent clause.
In formal writing, do all three deliberately and sparingly.