[tbelldesignco]

*As for the app I'd provide open registration and invited registration. 
Yes, the admin can choose to make registration open or close. There is really a lot of flexibility.

*And by the way,if a student lost connection while on the exam with a time limit, how will you handle it?

This is the only MVP version. People can log in and give exams for the duration of the exam. 

There is not counter cheating mechanism is in place.

This is a bare minimum working Exam application.

Really the only way to handle that is using AJAX handlers so JS/PHP to store the student's answers to cookies. Once the exam is completed and submitted you can clear the cookies used. I would also say I plan for the future in your initial development. If you are going to add higher level management to the system possibly down the road, then add the framework for that into the code now. That way you are not having to retool entire systems, modifying and upgrading the database and so on to add in an "School Administration" tier. These could be systems and protocols you add in now (ranks, rank access permissions etc.) that sit there until a time comes that you are ready for it. I just know with my devs, I made rookie mistakes not looking forward and having an "oh s***" moment when I had to recode entire features.