I was a SEN LSA last year in a secondary. Depending on the school and its SEN population you'll have a range of roles that span the special needs spectrum in ways you can't imagine before you're doing it.
Day-to-day job stuff included toileting, feeding, hoisting, physical therapy, speech therapy, scribing, interpreting poems, invigilating, confiscating sharp things (lots of this), nose blowing (metaphoric and literal), running social interference, academic prompting, social prompting, cheerleading, making sweatshirts and pop-up cards, sorting out friendship angst, mentoring, listening, being tackled in contact rugby, doing the cross country run, and - most importantly - laughing a lot. Especially during the cross country run.
My suggested interview question: "Will I be assigned to specific pupils or to general classroom support?" All of the progress tracking/assessment mentioned in previous posts is wildly easy if you're in the same classes with the same pupils week after week.