Why would you call "before" a preposition when it precedes a clause?

I'm new here & don't know all the etiquette & ins & outs, but I have a question about something posted in another thread.

Modern grammar, however, recognises that prepositions can take many different types of complement, or may take none at all. In the following examples we see prepositions which are taking different types of complement.

Let’s meet before the concert starts.

Let’s meet after the concert.

Take it out of the box.

I’ve never seen this before.

If you call "before" in "before the concert starts" is a preposition, what would you call "although" in "Although he didn't know the answer, he raised his hand"? I've been running "although" through my head, & I can't come up with an instance where it could precede a noun phrase. I'd call both "before" (as it's used here) & "although" subordinating conjunctions. If you don't call "before" a subordinating conjunction, what ties the two clauses ("Let's meet" & "the concert starts") together? If you tell me there's an understood "that," I hope you also tell me you're coming from a transformational grammar point of view. I'm old school & have hated transformational grammar since the day I met it!

(Also, I'd call the last use of "before" an adverb, but calling it an objectless preposition doesn't bother me nearly as much as calling the other one a preposition.)

I, The McGraw-Hill Handbook of English Grammar and Usage, and Grammatically Correct, 2nd Edition agree with you. "Before" in the first example sentence is a subordinating conjunction, not a preposition. It is a subordinating conjunction because it begins an adverb clause, "before the concert starts". The McGraw-Hill Handbook provides the following example:

I had finished my popcorn before the movie even started.

The Handbook indicates that "before" is a subordinating conjunction here. (And you'll notice that the sentence is coincidentally similar to the one you've presented.) Grammatically Correct also explicitly lists "before" in its list of subordinating conjunctions.

"Although he didn't know the answer" is also an adverb clause, so "although" is also acting as a subordinating conjunction.

"After the concert" is a prepositional phrase, unless the writer intended an understood (sorry!) "ends" at the end of the sentence, in which case the formation would be an adverb clause. As the sentence is written, however, the formation is a phrase.

"Out of the box" is definitely a prepositional phrase, as there is no verb present at all.

Lastly, I would also call "before" in the last example an adverb modifying "seen", unless the writer intended an understood "now" at the end of the sentence. Again, though, going by what is written, "before" is an adverb.