For those still struggling with this issue, I posted a solution awhile ago on the same topic. Please refer to this forum.
Marty Soupcoff
Posts made by Marty Soupcoff
I'm familiar with 1.9 and if you are on 1.9 as well wouldn't the combination of the Overall Feedback (simply tells them either to move on or re-take; more of a visual notification to the student) along with the standard locking options in the certificate, do what you want?
So an example would be, if you have two tests that they must get 70% or higher on each, in the certificate you set both quizzes as the dependent activities and 70% as the minimum passing. Then in the quizzes set the overall feedback for 100% - 70% to "Good job. Move on to next quiz" and 69% and below to "Please re-take before moving on". So if a student doesn't pass the first quiz, they would see that overall feedback right away and try again. They would have to continue to try until getting above 70% on both before being able to print the certificate.
If you are in 2.0, then you should be able to combine that with the new conditional activity feature. So a student who failed the first quiz, wouldn't even be able to attempt the second quiz let alone the certificate until they pass that first quiz.
Would that not work or am I still missing something?
What do you want to happen to the students that do fail? Do they just re-take the quiz?
If you want to get the message to the student that they passed or failed, you can simply add that to the Overall feedback of the quiz. That may be enough for your needs as I'm not sure what you mean by pass or fail in the "student's database" and what that would achieve.
Happy 
oodling!
If you want to block all other windows and applications, you may want to look into Respondus Lockdown Browser or Safe Exam Browser. There have been a lot of forum topics on this in the past so you may want to search the forums to gain some details or to see how other people have adopted them.