There are two common reasons for why student statistic are not showing up.
Reason 1: Student not enrolled
Please make sure your student is enrolled in your class and the right courses are added. If the class is not shown on their classes page (https://app.senecalearning.com/dashboard/classes) when the student logs in, then he/she is not enrolled and should click on the student invite link again, or join the class via the class code.
Reason 2: Internal school security
If the student is enrolled but no statistics are showing up then please ask your school's IT department to whitelist the following two domains: app.senecalearning.com and *app.senecalearning.com.