Sumdog offers over 100 K-8 math activities that teachers can assign to students to improve math fact fluency.
"In these activities, Sumdog learns about you as you work, and adapts its questions to suit." Here are the details about this feature:
> If you keep getting the questions right, they'll get harder automatically.
> If you have problems with a topic, Sumdog will help you practice by asking more questions. This means that you can use these activities with students of varying abilities, safe in the knowledge that each receives questions suited to his or her needs.