Raise your hand in a classroom with 70 students and chances are you won’t get called on.

Rewarding students a percentage of their grade for class participation is a great way to encourage lively class discussion. But many professors fail to realize there is a hard limit to the effectiveness of class participation grades: In lecture classes of 50-70 students, large class participation requirements are both unfair and detrimental to quality class discussion.

Despite their differences in size, there is a bias which exists in both seminar and lecture settings when it comes to class discussions: Professors tend to call on the same person.

Just ask Ray Win, a senior who spent several semesters as a teaching assistant for a large lecture course. Every time a student raised her hand, he would mark it on the class participation sheet and award points for the quality of the comment made.

“There is that tendency for professors to call on the same people, but it is not done purposefully. The professor sees their hand go up while everyone else is silent, and it just happens,” said Win.

When, on a good day, 20 out of the 70 people get called on in class, it’s unfair for the professor to let the guy in the front of the room talk three or four times.

The sheer size of class participation requirements makes it worse. When it’s a mere 5 percent, it’s no big deal; but when it counts for 25-30 percent of the grade in a lecture hall filled with ambitious minds, it encourages a rat race more than an intellectual class discussion.

Raise your hand and say something – anything – just to get your points in for the day. That’s when you get profound classroom comments that are simply regurgitations of previous comments, followed by some kind of tangent.

Having a TA count the number of times people speak up in class results in a preference for quantity over quality. Even when people are rated on the quality of the comments, it is exceedingly easy to game the system: If a quality comment counts for two points while an average comment counts for one point, just keep raising your hand to say gibberish, and you’ll end up on top.

Clearly, class-participation schemes are not scalable to a large classroom. They work well in foreign-language classes and small seminars where it is easy for the professor to keep track of faces, names and comments made, but there is a limit. So perhaps it is best to keep class participation requirements small when applied to large lectures.

And if you agree, then raise your hand – you might get some quality participation points for bringing this topic up for class discussion.