Between is for two. Among is for three or more treated as a group. The choice between English and Math. The debate among the four passages. This is one of the comparison-word items in comparison words, not a new family of rules.
Count the sides
Two named options, two people, two scores: between. A group of more than two where you are not pairing them off: among. Between the three tests is the usual miss. If you really mean pairwise choices inside a larger set, between can still work, but the ACT almost always wants the simple count.
Distance words that also split by job are in farther versus further. Countable versus mass nouns are in amount versus number. Diction overall is in word choice.
The bottom line
Two: between. A group of three or more: among.
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