Monthly continent/Yearly time period approach

I have found that it is wonderful to make everything as much as possible fit within the monthly continent theme (and ditto for using a time period for the whole year).  It provides additional potential for connection of concepts and ideas, not to mention it gives a cultural, historical, political, and geographical background for the artists, scientists, leaders, and book studied.

We found that separating the continents as follows helped ease the discussion of different continents with different numbers of countries and cultures within its borders (order is irrelevant in itself...we always tried to make the continent work as much as possible with the people we were studying or the book we were reading, or both, on those magical months :)...):
North America
Eastern Europe
Western Europe
Eastern Asia and Oceania
Western Asia
South America
Africa
(every few years, we include something about Antarctica with Oceania)

For instance, one month we studied the concept of "Freedom," with the focus on Western Asia.  We did an art project with glittering tiles, studied math from the viewpoint of "The Alexandrians," read about Muhammad and Buddha, and read "The Homeless Bird" and "Year of Impossible Goodbyes."  It was wonderful to see overlap and connections made between the different subjects and increased relevance of projects in that context!

For the time periods, we have, in the past, just used the break down of Susan Wise Bauer in her series "Story of the World": Ancient, Medieval, Early Modern Times, and Modern Times.  However, each group should apply and use this element as they feel it helps their group, not hinders them.

These two tools, using the continents and focusing on a time period for the year, allows the students to see the development of thought and style in art, science, and history in various places of the world and time periods, and, again, gives context and more connections.  However, they should be secondary to the importance of the monthly principles and different lenses.  For instance, if the book and the scientist are from two different continents, the mentors should decide whether the scientist or the book would be better understood by looking at the geography and history of a particular continent.

Also, as geography is in itself a lens, you could choose a continent solely on how different peoples within it or historically how it has fit within the theme.  For example, on the month where you are considering the impact of religion in society, you might want to study a sampling of different religions for your geographical/historical focus.  A fabulous continent to study with that would be Asia, with its diversity of religions.