As well as assessing students' understanding at any given time, you will also need to record their progress over time. Here are five suggested ways of doing this.
Even though Google now offers ten times more services for Google Apps for Education than they did at the beginning of the year, they still don't have a gradebook service. But the next best thing is a new offering from the free online gradebook system LearnBoost (previously reviewed here and here). LearnBoost can now be integrated into your Google Apps for Education account. LearnBoost can be found here in the Google Apps Marketplace.