Professor An Yu

Head of Basic Physics Courses, Tsinghua University

Teacher of the course Physics 2 of Xinya College

We often hear physics teachers at colleges and universities complain that students skip classes or play with their mobile phones instead of listening attentively in class. Some people agree with these complaints, while others blame that onteachers, saying their in-class performance is unsatisfying, and evenspout off abouthow to give physics lessons. Objectively speaking, it is true that many students often skip classes, the attendees are absent-minded, and some teachers are not attractive. The current learning environment is very different from that hundreds of years ago. In the past, it was not easy for students to grasp knowledge in other ways than attending classes. Now, however, since there are many ways of learning, it is natural for students to skip classes. I remember that there were already a lot of reference books about 30 years ago when I was a student. At that time, I felt that sometimes reading books by myself was more effective than attending classes, because I was not restrained by the schedule of the teacher. Nowadays, acquiring knowledge is much easier. With little effort, you can find what teachers have taught with cell phones and browse through them at your own pace anytime and anywhere. Thus, the importance of the classroom teaching is greatly reduced.

Some people have proposed that teachers should upgrade teaching methods to improve the efficiency of classroom teaching. But how? If teachers still stand on the podium to give classes, will the efficiency be improved substantially? We can indeed take some measures to reduce absenteeism, such as calling the roll, but isn't it a waste of time if the attendants do not listen to the lecture? What if students are not interested in the teaching because the teacher is incompetent? Can we solve the problem by replacing him/her with a more competent one skilled at teaching? I once listened to a physics class by a famous professor at a famous university in China. The teacher clearly explained the concepts andemphasized the key points witheasily-understood words and neat writing. The class was excellent. Then, how about the students' feedback? They unanimously praised the professor though they could not remember what was taught.

We universally acknowledge such a class is perfect. Ifa class as great as this one is not attractive to students, let alone others. To our disappointment, even such a perfect class failed to achieve the expected effect: many students showed poor performance on this course. The teacher once complained about his students in an open letter because of a high failure rate. This is understandable — the teacher was competent, and his teaching was well-received, then the students themselvesare to blame forthefailure. Actually, it is a misunderstanding that as long as a teacher gives wonderful lectures, his/her students can learn the course well. Many experienced teachers know that learning and teaching are two things. Some people may think that wonderful lectures can at least attract the attention of students. Yet, the idea itself is very subjective. Psychological studies tell us that students areusually let their minds wander1/4 of thetime on average no matter what course it is. What's more, physics is more difficult to learn. It is strongly logical, requiring students to stay focused in class for 45 minutes, which is hard. Big data studies show that concentration generally lasts about ten minutes. The content of a physics class is highly coherent. Once your mind wanders, it will be very difficult for you to keep up with the pace of the teacher again. When that happens, it is useless to try to refocus. This tells us that no matter how good a teacher is, students will lose concentration, which is an inherent defect in classroom teaching.

The quality of a teacher should have some impact on whether students learn the course well or not. A good teacher may attract students to like the course, but for a course like physics, that is far from enough to improve the efficiency of classroom learning. Physics learning particularly requires thinking and understanding. Under the mode of teacher-centered classroom teaching, students have to always follow the teacher. In this way, students cannot think freely and calmly, which means that they have to reflect on what they have learned after class. Thisgreatly reduces the efficiency of classroom learning. In the current situation where the class hours of physics are seriously cut down in most colleges and universities, teachers have to teach a lot in class. Once you do not understand a concept or method, it is almost impossible for you toknow what the teacher says next, let alone take time to think. Even if a student really follows the teacher from beginning to end, does he/she certainly master all the concepts and content involved? There is a gap between learning from others and by oneself. Independent thinking and exercise are necessary for truly understanding physical concepts and methods. Some students can basically follow the teacher in class, so they mistakenly think that they have understood what is taught and do not seriously think and review after class. It is not until the exam do they find that they have not mastered what is taught ina real sense. Therefore, the defects of classroom teaching are essentially caused by the mode featuring active teachers and passive learners.

The teacher-centered teaching mode has led to another universal illusion that the quality of teaching depends on the quality of teachers, which is often equalized to the teacher's performance in class. Teachers, teaching regulatory agencies, and even ordinary people tend to evaluate a class according to the performance of the teacher. This is a result of a teaching-dominated, rather than a learning-dominated philosophy. A wonderful lecture just means that the teacher is competent, but does not necessarily mean the students can really master the contents imparted. There is still along way to go before students can getgood academic performance. No matter how wonderful lectures a teacher gives, many students cannot learn well. If the number of poor students is beyond the tolerance of the teacher, generally, the teacherwill criticize those students for not working hard, not listening carefully in class, taking little after-class effort, or having poor learning ability. Anyway, it is the students' fault, because, in the eyes of bystanders, the teacher's performance in class is impeccable. But if we do not forget the main purpose of teaching — to help students learn well, we can understand that the teacher's performancewill not directly lead to satisfying learningoutcomes. In other words, the quality of teaching has little to do with the teacher's class performance.

Sometimes, we may find that good teaching is not helpful to students. Teachers should not focus on how to perform well in the classroom, but earnestly consider how to make students learn more. A teacher may gain a good reputation for his/her excellent lectures, but it can only prove that the teacher is an outstanding speaker, which is not exactly his/her duty. The main responsibility of a teacher is to help the students learn well. As a matter of fact, no data support the assumption that a teacher's performance in class inevitably influences the students' learning performance. The data against such an assumption is too many to enumerate. Here is an extreme example. The graduates of the Southwest Associated University (Tsinghua University, Peking University, and Nankai University) in the 20th century boasted a particularly high success rate. Of course, there are many reasons behind that, such as students' determination to work hard to serve the country faced with a calamity.In terms of the effect of classroom teaching alone, at that time, teachers generally spoke dialects, so their lectures were not wonderful at all, and students could not even hear them clearly. But this did not affect students' learning outcomes.

Therefore, teaching performance cannot determine whether students can learn a course well. We should never forget that students are principal, while teachers are just auxiliary. A good class in a real sense should depend on the students' gains rather than the teacher's performance.The evaluation of teaching quality should focus on one thing: how much do students gain in the teaching process? Both experts and students may take it for granted that good teaching naturally leads to satisfying outcomes for the students. This is actually an obvious misunderstanding. To learn physics well, the fundamental lies in whether the students can independently think over and understand the concepts and thoughts and master the methods through practice, rather than listening to what the teacher says in class alone. If a teacher performs well in class, the students often feel good about their classroom learning. However, if they spend little time in after-class thinking and exercise because of this, their learning outcomes will be dissatisfactory.

One study reveals, from another aspect, the serious drawbacks of our current learning approach. As physics is required for the college entrance examination, Chinese students begin to learn the subject atthemiddle school, while American students generally start to learn it attheuniversity. A comparative study of physics education in the two countries shows that the academic performance in physics of Chinese middle school students is significantly better than that of their counterparts in America, which is as expected. However, another result is surprising. There is little difference between Chinese and American middle school students in scientific reasoning skills. As we know, a very important task of physics education is to improve students' scientific literacy. We always think that as long as they can learn physics well, their scientific reasoning skills will naturally improve, but this is not the case. For students, doing physics exercises is different from solving physics problems. When solving a problem, they do not use the scientific methods learned from physics, but the experience they have accumulated. This shows that the expected goals of physics learning envisioned by course designers have not been achieved. What is wrong? It is unfair to accuse middle school physics teachers of bad in-class performance because students are able to do physics exercises, which means the teachers explain relevant content clearly. Some people say that physics teachers should impart not only knowledge but also physical ideas and methods. The problem is how to make students understand so much through physics courses? At least the current learning method does not reach the goal.

Daniel Kleppner was a physics professor at the Massachusetts Institute of Technology (MIT). He was very successful in both physics research and teaching. His classes were very popular with students, and he himself enjoyed his classes. Many years after his retirement, he came to Peking University to give a speech. What impressed me deeply was his reflection on the way he gave classes. He said that if he had another chance to give mechanics lessons (he once taught mechanics at MIT for years), he would do it in a very different way from what he used to do (standing on the podium). In fact, many people are aware of the drawbacks of the teaching-centered approach, includingProfessor Mazur at Harvard University, who therefore put forward the concept ofpeer instruction. Many foreign scholars have done a lot of research about teaching methods and put forward many learning-centered modes, such as flipped classroom, inquiry-based learning, and research-oriented learning. Many domestic professors have also realized that we should change from being "teaching-centered" to "learning-centered". I have been a teacher for years. With the accumulation of teaching experience, I had a better grasp of physics and explained physics concepts more profoundly and comprehensively. My lectures became smoother, of which I felt very proud. I believed that I taught well, so my students learned well. But each test or exam told me this was not the truth. Sometimes, even some knowledge points particularly emphasized in class were not well grasped by the students. The degree to which students understand and master was often not in line with my expectation, which urged me to reflect on the "teaching-centered" philosophy and try a hybrid learning mode under the learning-centered philosophy. But many professors do not agree, especially those with excellent in-class performance. They overestimate the effects of their lectures and enjoy them. In my opinion, it is just self-complacence.