My 7th graders recently worked on a test-prep activity where they were asked to read several primary source documents that were dated from different time periods. Then, a question asked something like, "In the passage from the 17th century, what was the main idea?" ACK! So many kiddos didn't know whether the 17th century meant the 1600s, the 1700s, or the 1800s. The next day as we were discussing this, I realized that over half the class had NO IDEA how to tell what the century is, so I creat