If you just want to put a lock on the door, this is one of the things that is being developed for Moodle 2.0, and there is the conditional activities patch for earlier versions of Moodle that might be worth investigating.
However, from an educational point of view, do you really need to lock the door. Surely the quiz tests the student's understanding of the reading. The student will only be harming themself if they did not do the reading, and managing your own work is an important thing to learn. Also what if the student's friend went to the reading and printed out two copies so they could read it on the train home. Both students have read it, but Moodle will not know that.
However, from an educational point of view, do you really need to lock the door. Surely the quiz tests the student's understanding of the reading. The student will only be harming themself if they did not do the reading, and managing your own work is an important thing to learn. Also what if the student's friend went to the reading and printed out two copies so they could read it on the train home. Both students have read it, but Moodle will not know that.
Thanks for your excellent response - and that's a good point. I agree that in principle we don't want to be locking things down and need to engender a sense of personal responsibility in students. There are some situations though, where it could be helpful It is not uncommon in junior high at least, for students to attempt the assignment before doing the pre-requisite reading. Maybe once this pre-requisite reading time is sufficiently habituated in students, I can then unlock it and see how they go.