I am a lecturer in charge of a course with over 250 students and several TAs. The TAs are partly responsible for grading the homework assignments. Since these are assignments in programming, no two submissions are identical, so it is impossible to cover all possible cases in the grading guidelines, and the grading has some subjective element.
I noticed that one TA is consistently stricter than the others. For example, if the guidelines say that "code efficiency" is worth 20 points, then this TA would deduct 15 points when the code is inefficient, while the other TAs would deduct only 5 points for a similar issue. A potential problem here is that it might be unfair to the students in the strict TA's class, but this can be solved by allocating the assignment task "horizontally" (each TA grades all 250 submissions in some of the assignments) rather than "vertically".
But I have a different question: I noticed that students who are graded more harshly, take the feedback comments more seriously, and tend to become better programmers. So, rather than just being "fair", I would like all TAs to grade in a stricter way - for the sake of the students. The problem is, most TAs are not motivated to grade strictly - they gain nothing from it; all they get is having to handle students' complaints and appeals, and risking lower marks in the students' feedback (since the students do not understand that it is in their favor until after they graduate).
The TAs are not lazy - they do put a lot of effort in teaching and helping students; they just don't like to be the "bad guys" who give low grades. How can I motivate them to give stricter grades?