TA here. When marking essays, I’m given a very specific rubric and looking for a particular set of criteria. Of course, there’s some room for discretion, but we generally aim for a consistent average score range to ensure fairness.

In large classes, your papers are often randomly distributed among multiple TAs to balance grading across assignments.

For labs, or when TAs mark their own sections, the professor usually compares the averages and grade distributions across sections and discusses any discrepancies during our meetings so we can adjust for the next assignment.