I worked as a tutor during my uni days.
Overall I enjoyed the experience, but assignment marking is hell. I've always joked to other tutors...If Dante (the poet) had been familiar with the life of a tutor, he probably would have added another level of Hell to his Inferno. The condemned would sit for all eternity and read one mediocre assignment after another, meticulously correct every mistake, agonize over every mark, and then throw each graded paper into a fire.
There are few things more discouraging than finding yourself at 2am reading the 20th assignment in a row on the same subject when you know that there are 50 more to grade. To mark conscientiously requires a draining degree of sustained focus, and after all of your effort, you know that only a few of the students will give more than a minute’s attention to the comments that you have painstakingly written with your aching hand.