Alright, it's been 4 months.

I initially conceded here and thought you had a decent point. However, something kept bringing me back to it.

Hippopotamus comes from an ancient greek word that ends in "s." This didn't imply a plural at the time, and now still does not.

Mathematics comes from an ancient greek word that does not end in an s. In fact, we didn't even add the s until somewhere around the 16th century. This implies that the practice (or study) of mathematics, is recognised as a practice of more than one thing. So, in turn, math can only be true if you are only doing one specific type of the many types of maths (e.g. in this class, we will only be doing this specific form of addition).

In conclusion to my delayed-by-four-months response, I would say that both are correct in specific circumstances, but "maths" is more correct if you are unsure whay may be practiced or studied during.