Personally, think the Ammies got it right, again: It's "Doing Math" and "My Maths were terrific" (regardless, no matter what, their glass is 3/4 full when conversing with them over the phone :). Reading densnaps' circa 1793 dictionary, maybe it would be better to make the plural "mathae", but then some would confuse this with the phonetic for a Judo term though that is correctly spelled as "Mate" and that is very much Aussie ;>)

Language is such fun, no matter "To S or not to S, that's the question".

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PS, and "mathematicks" is the best... some get a tick from math :P

From the way that dictionary reads, I'd almost expect to hear/see "Mathf."

As an abbrevation of Mathematics, Math is better than Maths. The s at the end is not needed in order to convey the proper meaning.
When I see the word "Maths" I expect someone to be referring to multiple equations as opposed to a single subject.

To UK English speakers, Math would be an abbreviation of Mathematic (a spelling mistake in UK English). Mathematics is the science of calculations. Mathematics is a plural word and there is no singular. Without the S it's just not a word in English, UK/Australian/NZ/SA...
Might explain why Americans don't wear trousers,

So, as a framework or subject term "Mathematics", can be fairly seen as singular, or, after all when you go to the fancy fair (no s), do you go to one or more events, and when going to a pop concert, is there 1 act or more acts...

As I said, language is fun, and in New Zealand they where no wear [homophones galore in Inglse] trouser lengths (singular or plural?) just as in that image with a bow tie and long socks. Just aks :D

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Or as we call them in the U.S., pants. Which I once found to my great embarassment has a completely different meaning in the UK.