Comment Open to options? (Score 1) 120
There have been plenty of recommendations for Moodle, but just to throw it out there... it's not open source, but GradeConnect is a hosted course management system and is designed to do exactly what you're looking for (and a whole lot more) and has a free version. I used to do some development work for GradeConnect 6+ years ago, so I know the folks who run it and they're all educators. It really is a system designed by teachers, for teachers. Worth checking out at least!
http://www.gradeconnect.com/