We’re told in school to never end a sentence using a preposition.. why? I ran into the answer.

It was John Dryden who first promulgated the doctrine that a preposition may not be used at the end of a sentence, probably on the basis of a specious analogy to Latin. Grammarians in the 18th century refined the doctrine, and the rule has since become one of the most venerated maxims of schoolroom grammar. But sentences ending with prepositions can be found in the works of most of the great writers since the Renaissance. English syntax does allow for final placement of the preposition, as in We have much to be thankful for or I asked her which course she had signed up for. Efforts to rewrite such sentences to place the preposition elsewhere can have stilted and even comical results, as Winston Churchill demonstrated when he objected to the doctrine by saying “This is the sort of English up with which I cannot put.”·Sometimes sentences that end with adverbs, such as I don’t know where she will end up or It’s the most curious book I’ve ever run across, are mistakenly thought to end in prepositions. One can tell that up and across are adverbs here, not prepositions, by the ungrammaticality of I don’t know up where she will end and It’s the most curious book across which I have ever run. It has never been suggested that it is incorrect to end a sentence with an adverb.

Source: TheFreeDictionary.com (click title for page)