> Grading a multiplication test in grade school might be quick and mechanical but grading trig and calculus is not.

I gravely disagree. I spent a lot of time grading calculus exams at universities, and it is a quick and fairly mechanical procedure. A group of five can churn through three hundred final exams in a working day.

Answers in maths are quite uniform and contain a few sentences which can be quickly judged by how correct they are. Calculus and trigonometry might be difficult for the students, but for someone who has taught it a few years, it is absolutely straight forward to recognise correct solutions.

Grading say, English short stories or essays is a completely different thing. There are a lot more sentences, which have to be analysed grammatically and semantically. You have to judge how coherent the student is, which is a non-local property. Does the end match the beginning? What is the student trying to say? Do they use a clear language? If not, what feed-back can you give that will improve it. What literary effects does the student command? Allusions? Irony? Foreshadowing? Contrast?

The answers are highly personal and even using rubric grading every one is a non-trivial judgement call.

I believe that the nature of the tasks and subjects have a bigger impact on how much time it takes to grade it, than how efficient the individual grader is. I have experience correcting in groups where I have been able to compare grading speed. Yes there are differences between how fast people grade, but they are minor, and often speed is inversely correlated with quality (of feedback given to the student).

> Some people are more effective/efficient/faster than others.

Learning takes time. Students learn by doing different activities related to the topic. Sometimes listening to the teacher explaining, sometimes working on problems of their own. In mathematics, it is easy to find good examples to demonstrate and problems for the students to work with. Other subjects, it is much more difficult, and requires prep work.

Taking less time to prepare will usually mean worse teaching. For instance I had a history teacher who would just put on recordings from History Channel. He thus had to spend little time preparing the lessons. But the learning outcome was not the best.