I don't remember if it was a formal study but somebody has asked students at the beginning of the course what grade they _think_ they'll get and at the end it fit very well. Basically all students try to make a particular grade with the least effort, since that's what they are incentivized to do.
Indeed, since the evaluations are handed out before the final grades are tabulated, they can only be based on expected grades. But expected grades are still a better performance metric than a coin toss.
