It is common for professors to base a student's grade in part on the degree to which he participates in class discussion. This policy seems to me to raise serious moral issues. The grades I give my students purport to measure how much of what is taught in the class they know. By giving a higher grade to those who participate more I am bribing them to help me to teach the class. To put the point more strongly, I am getting them to help me by offering to lie to their future employers about them, to overstate how much they learned as a reward for their assistance.
This objection would not apply if I were using their classroom participation merely as evidence of how much they had learned, grading them up for participation that provided positive evidence, down for participation that provided negative evidence. But that is not what professors who give credit for class participation do, or say they do.