I know from my own education that the information understood from traditional lectures is usually much less than what the teacher is trying to convey. This is especially true in "hard" lectures such as mathematics and physics.

Therefore me and a group of students created a tool for the teacher to visualize how many of their students understand what is being said at every moment of the lecture.

Now we're starting to wonder if this is a problem for other students/lecturers/schools as well. What is the efficiency of a lecture? How effective is the transfer of information? How large proportion of the students do actually understand what the teacher is talking about? Is there any research which has tried to estimate this?

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    $\begingroup$ I just wanted to point out that understanding often lags the information input. Sometimes the material just needs to sit in there for a bit to assimilate. Also, there's a memory decay starting from the moment one is exposed to some piece of information. Once the student is out of the lecture the student will begin to forget things exponentially fast. I would think understanding would follow a similar pattern. $\endgroup$ Commented Apr 24, 2014 at 9:48
  • $\begingroup$ What exactly is your tool? $\endgroup$ Commented Apr 25, 2014 at 2:39
  • $\begingroup$ The MOOC companies and others offering online education have research on this: online lectures usually include easy quizzes in the middle. These often reveal that students did not grasp what the instructor just said (and you can assign blame to either party if you choose). I can't quantify "often" for you, but the education providers probably can. $\endgroup$
    – user173
    Commented Apr 25, 2014 at 4:06
  • $\begingroup$ This depends A LOT on the skill of the lecturer. I have lectures where I can understand almost everything (only needing to refer to notes for definitions), and lectures where I understand virtually nothing (I've stopped attending these ones). And this has held even when I've had different lecturers teaching the same material. $\endgroup$
    – Nico Burns
    Commented Apr 25, 2014 at 11:53
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    $\begingroup$ @RyanMcGaha, our tool is located at getit.csc.kth.se. And ironically, even the name is very similar to the tool that Adrienne mentions in an answer below, but I can assure you that we didn't even know they existed. $\endgroup$ Commented Apr 25, 2014 at 15:48

2 Answers 2


Question: What is the efficiency of a lecture? Answer: Assuming that the learning comes from studying the notes generated by the lecture, students can recall about 80% of a list of facts for a day or so, and then this declines -- often down to low levels like 40% -- after a few weeks.

Obviously, difficult concepts are not learned as well to begin with, and concepts that are repeatedly tested are retained longer.

Some classic studies of this issue are comparing retention of straight lecture vs alternative, more active teaching. Some examples:

  1. Pausing during the lecture can increase retention.
  2. Memory of studied material increases with testing
  3. General overview on how to be more effective than lecturing in engineering

Your tool is a good idea, and rather hot in edtech right now. Apps like "Geddit" are designed for K-12 classrooms. And instructors who want to assess understanding can use clickers and ASK how students are doing.


  1. Ruhl, K. L., Hughes, C. A., & Schloss, P. J. (1987). Using the pause procedure to enhance lecture recall. Teacher Education and Special Education: The Journal of the Teacher Education Division of the Council for Exceptional Children, 10(1), 14-18.
  2. Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning taking memory tests improves long-term retention. Psychological science, 17(3), 249-255.
  3. Prince, M. (2004). Does active learning work? A review of the research. Journal of engineering education, 93(3), 223-231.

As a recently "retired" student, this is my perspective:

You seem to be tacitly implying that the efficiency is somewhere around "very poor". If so, I am certainly not surprised.

I found very early on in my mathematics education that if I went to a mathematics lecture in which the material was entirely or almost entirely new, I would comprehend very little of what was said. I would perhaps be able to follow the first few (largely preliminary) definitions and arguments given by the professor, but after that I would get progressively more lost. By the end of such a lecture, I was usually looking at something vaguely reminiscent of Greek, and not at all appealing :)

So what did I do? I took up the habit of learning things entirely before the lecture started. My goal was always to come into the lecture hall having a solid grasp of all the topics covered in that day's section. I found that this helped enormously.

I don't think it's fair to say that "lectures are worthless". But, at least for me, the primary benefit from lectures was seeing a proficient expert work examples that I already had a rough idea of how to solve. I don't think anyone but an intellectual daredevil could simply walk into a graduate-level mathematics class and learn the material cold, with no background whatsoever. Very few people absorb concepts with such rapidity, and even fewer retain them after such brief exposure.

I definitely believe that lectures have the potential to bestow massive intellectual benefits on their students, but those students have to engage at an appropriate level. Passive listening, at least in mathematics, seems rarely to work (if at all).


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