If it wasn't an essay question, you could use interactive with multiple tries which has the desired behavior.
But if these are essay questions, only the teachers can know if they are correctly answered or not...If you use multiple tries and let each attempt build on the last, that might work. The teachers just would ignore the questions that they had given full points for...
I presume that you are wanting to Moodle to only let them repeat the questions that they have not received 100% on? I imagine that would take some extensive coding.