If you think your student's account is not at an appropriate level for them (or if they haven't used it for a while) they may need to do a reassessment (previously known as recalibration). Don't worry, they won't lose any of their hard earned stars! It just reassess the account to ensure it is working at the right level for them.
Please login to the Teacher Dashboard and follow these steps:
Select Analyse > Understanding
Select the class the student is in.
Click Start New Baseline with whole class and select the student/students you'd like to reassess.
OR, select the student's name on the left hand side and then scroll down to the bottom of the page and click start new baseline assessment for X to start a baseline assessment for just that student