We use Yacapaca with our KS3 students at school, have been doing so for a couple of years now.
What or who is Yacapaca?
Yacapaca is an online system that is free to schools. We use it for setting homework, the students do a quiz online each week.
You can choose from lots of existing quizes or make your own. The system marks the quizes for you and shows the class's marks on one page.
Free?
Go to www.yacapaca.com/ and sign up for free.
No internet access?
We printing paper copies of the tests for students without internet access and reinforce the rule of 'don't leave it until the night before' every lesson.
Accuracy?
I'm not sure it's amazingly accurate as anyone can make the quizes but it's not bad.
Admin
Adding classes is easy, simply copy and paste a list of students into the page. Adding quizes is also easy.
Nice touch
There's a 'Whiteboard' button that shows the 'leaderboard' from a quiz, it slowly slides the students name into their positions creating an air of suspense!