Try this out. It's more complicated than I had previously thought:
The seven-continent model is usually taught in Western Europe, Northern Europe, Central Europe, Southeastern Europe, China and most English-speaking countries. The six-continent combined-Eurasia model is preferred by the geographic community, Russia, Eastern Europe, and Japan. The six-continent combined-America model is taught in Latin America, the Iberian Peninsula, Iran, Greece and some other parts of Europe. This model may be taught to include only the five inhabited continents (excluding Antarctica)[17][18] — as depicted in the Olympic logo[19].
The names Oceania or Australasia are sometimes used in place of Australia. For example, the Atlas of Canada names Oceania,[10] as does the model taught in Latin America and Iberia.
The rest of the article can be found on Wikipedia here:
Continent - Wikipedia, the free encyclopedia
That should pretty much solve the argument, but getting them to accept it is another thing. Good luck!