Exactly what problem will this solve? 
Problem: if a teacher returns to his earlier recorded comment/response on a pupil's  assignment answer, he can't see or hear his comment again from the pupil's assignment answer.
For whom do we solve that problem? Teachers and schools
How will we measure success? Better feedback processes in assignments. Better learning.
What alternatives are out there? NR
Why we are best suited to pursue this? NR
Why now? Basic need
 
User story:
As a Teacher,
I want to Be able to record my comment on a pupil's assignment answer - and play it again. (Recording comments is easier and faster for me and those of my pupils that have reading difficulties get a lot more from my recorded comments than from my written comments. Many pupils who don't have reading difficulties prefer my recorded comments. )
so that I Save time and can be more ascertained that my pupils actually see/hear my feedback and learn from it.

It's important to describe the goal and the reason separate. The reason is the most important one, and is often not communicated. Users often only tell what they want, not why they want it. It's also important to break down huge requirements into many users stories.