Comprehension Failure or Short Term memory Failure?

I experimented with the undergraduate teaching process a little. I wanted to see how much attention they paid during the teaching session and how much they comprehended. Since they never made any notes while we taught, one had to presume that they either already knew whatever we taught them, or understood the stuff so well that they did not have write anything down. When I started a small group teaching session, I told them they would sit for a small test at the end of the session. I told them a correct answer would get one mark, a wrong answer would get minus two marks, and no answer would get zero marks. They did not disagree. I taught them at a speed at which they could understand everything. I asked questions in between and answered those questions myself if they couldn’t. They had some difficulties, which I solved. There was that guy who kept turning the angles of his lips down and nodding his head throughout the session, as I have seen actors in American films do, to show that they knew what was being said better than the person who was saying those things. He was not just a ‘nodder’, but a ‘superior nodder’. For those who don’t know what a nodder is, let me state that a nodder is a person who nods his head much more than an ordinary person does during a teaching session. I gave them a break of five minutes after the session, during which I composed five multiple choice questions, each with a single correct answer to be chosen from four possible answers. I collected the answer books and corrected them immediately in front of them. I returned the answer books without reading out the marks aloud. That was meant to avoid embarrassment for those who scored badly. They promptly checked out one another’s marks anyway. Out of maximum five marks, the ‘nodder’ got -3, others got -1 or zero, and one of them got 1. The ‘nodder’ turned out to be a pseudo-superior-nodder’. The others were terrible. I had really asked quite simple questions based on what I had taught them barely 5 minutes ago. It reminded me of the Dean asking me about a large number of students (more than 20) failing in obstetrics gynecology in the University Examination in the previous batch. The explanation for these doing so badly was perhaps the explanation for those failures in the University Exam too. If any of my readers is a pure educationist and will tell me exactly what is wrong with these presumably bright young students, and how to correct the problem, I will be much obliged.