One thing you can do is set up a variable on the last page of each module then when they try to access the final assessment you can set the condition to only go to that page if the variables for each page are met. If the variables aren't set then use the Else tab to send the user to a page that tells them they must complete all the modules. You can check the variable values to see which module was not complete and update the page to tell the user the module.
Hope this helps
