People had limited energy, even wizards.
Ever since the Weasley twins had arrived at Hogwarts, Professor McGonagall had considered finding a suitable student assistant.
Her duties were already extensive: preparing lessons, grading homework, adjusting schedules for seven year groups, dealing with Gryffindor House students' mishaps, liaising with the Ministry of Magic, reviewing and approving purchases of school supplies, examining professors' requests, surveying graduates about employment, coordinating with other schools, and reviewing and re-reviewing exchange student applications...
That workload, plus the occasional emergency, was more than a professor could handle even without teaching duties. And with the Weasley twins around, emergencies had become routine.
But a suitable assistant was hard to find. As Hogwarts's deputy headmistress, openly hiring one when Dumbledore had none would practically amount to accusing the headmaster of neglecting his work. Besides, the assistant's position would be difficult to define...
Students were better candidates. They learned quickly, cost little, and were unlikely to clash with other professors after taking on assistant duties. The professors would have few objections, either.
The problem was finding the right student. Even professors choosing teaching assistants had to assess their character and knowledge. A student working in Professor McGonagall's office would require still more scrutiny.
Character, temperament, ability—none could be lacking. Background mattered too. She absolutely could not choose a student from the most vocal pure-blood faction; some people might take it as a sign that Hogwarts was favoring pure-blood wizards...
So despite having the idea, Professor McGonagall still asked the Gryffindor prefects to help with some of her paperwork. Their help was limited, though.
Students could not become prefects until their fifth year, when they faced the crucial OWLs. Seventh-years had the NEWTs and had to think about jobs and internships. By the time a sixth-year finally learned the ropes, she would