Subset tests can be run through the Details of a student's test.
You can select any questions to run as a shorter test. When you complete the subset test, the Pie Chart and Class Totals Report will both show the results of the subset test as if the entire test was given.
So, if we were testing the 26 Uppercase Letters, you could choose 20 subset test questions. If the student got 7 questions correct during the subset test, the pie chart on the Home Page would update to show that the student had answered 7 questions correctly.