I know there are several different ways someone can "fake" what a page shows by modifying its HTML after its been received by using tools like Inspect Element.
Let's say kids have been using this to their advantage and "changing" grades on their online gradebook.
Let's say that I am the director of the school.
What could I do to prevent this? Asking parents to refresh the page seems redundant, so what are other ways to make sure parents are getting the real deal?
You can't ever stop someone doing this, so don't try to.
Instead think of providing the same details in other forms - an email directly to the parent, a letter (the student could still copy/replicate the letter but it's a lot more work to do so), published grades at the school, etc.
In fact, a nice complicated printed certificate wouldn't cost much to produce, gives the student something to be 'proud' of to show off, can be framed etc. The little cost involved plus the complication of trying to replicate/forge this would be sure to stop all but the most determined students (and those are the ones who in my experience get the best grades anyway).
As for fixing the 'page' itself, some 'simple' changes you could make are such as displaying the grade as a semi-complicated image, rather than just text, or having 'parent' logins, which you'd hope they didn't share with the students.
