When students find a skill difficult, Sumdog skips it and comes back to it later. This is called a hard skill.
When a student has 3 or more Hard Skills, Sumdog switches to revision mode. They'll be asked questions on things they have already completed, mixed with occasional questions from their hard skills.
Once this student becomes more comfortable with the questions from the Hard Skills, they will start focusing on that skill again, with the aim of completing it.
If your class is subscribed, click a student's name on your Overview page, and see their individual Hard Skill count and report.
With the Administrator Toolkit, you'll be able to run a Hard Skills report for your classes.
Tip: If a class is struggling with a particular skill, run a challenge focusing the students on this skill.