A Lie

The passage you've provided seems well-written for the most part, but I've made some minor corrections and suggestions for improvement:

The lecture hall buzzed with chatter as all the students waited for the arrival of the professor. Soon, Professor Thomas strode to the front of the room, his stern expression hinting at the seriousness of the situation. He cleared his throat, commanding attention.

"Good morning, class," he began, his tone dripping with a mixture of authority and frustration. "I've just finished grading the derivative assignment, and I must say, I'm not surprised by the results. Like I told you previously, this assignment was only to test your level of aptitude and skill, to understand where you stand in terms of your grasp of mathematics. As expected, most of you have fared badly."