Hello Stef, I am familiar only with MOODLE 1.9. So, the contribution of Viral its an option for sure.
- Well, in case of the MOODLE 1.9, in the lesson there is a dependency option where you can define what you want. You can use it if you set all the 4 essay subsections as 4 different lessons, each dependent on the former grade lesson.
- The other option is to set the menu to show only if the grade is better than a value (you can do this in the lesson configuration), and the essay will appear only in the menu (see note 1). Of course you have to choose the path of your lesson in order that the student doesn't found the essay with the buttons.
I suggest that you use a map to design your lesson: cmap tools can help.
I hope this is helpfull. Good work. António
note 1: you must notice that the essay questions doesn't appear in the menu, but if you put a branch table called "essay question" and choose the button to go to that question...