GoGuardian's support website is an excellent resource for finding answers to commonly asked questions: Teacher Support Center
Not seeing a student's screen?
Possible Reason #1: Lag time
Solution #1: Give it a minute
Possible Reason #2: "Student not found". A common reason for not seeing your student's screen in your GoGuardian active session is if a student joined your Google Classroom using their personal Gmail account and then you uploaded your Google Classroom class into GoGuardian when you created the GoGuardian class.
Solution #2: Either have your student do this or do it for him/her: 1) unenroll student who signed in using their Gmail account from the Google Classroom, 2) re-enroll student using their PISD email address.
Are you seeing two screens for a student?
If you see two screens for a student, one in which states "Monitoring is Restricted", this means that the student is also logged into another device either at home or on a computer at school. GoGuardian cannot monitor the student's activity on their personal Chromebook at home or on a PC.