Today I visited a AP chemistry class in a high school. I found this class is apparently test driven. The teacher first let the students took a test for 15 minutes. And then coped with students’ individual questions and worksheet related issues. Then he began teach students the rules and tips to get right answers to the questions. Once a time, a student asked when they would do laboratory. The answer was “maybe next week”.
The whole class last 90 minutes, which is twice long of class in China. There was a 5-10 minutes break during the class. There about 30 students in the classroom. The topic of this class included Ionic bond,Covalent bond, Polar and non-polar Molecular, Melting point, Atomic properties. The main objective is to learn how to judge which Molecular have higher melting point or stronger bond for the quiz questions. This class was a teacher-dominated class. Teacher used most of the time to lecture the “powerful” tips to solve these type of questions. About 20 students seemed listen carefully and 10 students enraged in the conversations by asking questions. Teacher usually addressed students questions immediately sometimes said he would addressed that question later. There were several times students want to ask questions, but the teacher went along with the important tips and principles.
To my surprise, there was a student had nothing to do and lay on the ground listen Mp3. The student said something to the teacher before class, the teacher just let him go. This will never be allowed in Chinese classroom. There are some student hard to like too in China, but mostly they will not put their feet on their desk or sleep on the ground. The teacher will never allow this happen too.
While the teacher also tried to help student understand what factors affect the strength of a bond. He wrote down the Electric force formula on white board. He also used an analogy of 10 toy between boys and girls to explain Polar and non-polar. I am very interested in this representation, it tell me something about the teacher’s stratiges to convey the concept to students, researchers name this knowledge as Pedagogical Content Knowledge. This representation do help to understand polar and non-polar, the teacher said that think about a group of boys have 5 toy and the girl group also have 5 toy, then it is equal, so in this case the bond is non-polar band. As to polar bond, the teacher let students thought about boys had 7 toy while girls only have 3 toy, this is polar bond. As to ionic bond, the boy just got all the toys while girls have no toys. I agreed this analogy could convey some important features of the concept to students. But if you think carefully, this representation also has fatal limitations and even wrong. First, Electron pair does not “belong to” each side but “shared”. Second, it is dynamic not static. Third, it is not how many electrons each side have, but how frequently it appears around. Well, teacher can use analogies as middle models to help students learn, but it is also necessary to know the limitations of every middle models and move along to the more scientific models.
On my road home, I watched a TED show Dan Pink: The puzzle of motivation. The speaker talked about higher motivation(big award) can impede or even kill creativity(e.g. developing new software). I want to say it may also be true in education, while teacher highly motivated to prepare students to get better score, they will decrease the variety of teaching methods until only lecture left. It had happened in China, US would not like to fall into the same old trap again.
2014-04-23
When we are developing an instrument to measure teachers CK, Ben gave us a good analogy of chemical reaction. It is much better than the above chemistry teacher.
The force holding bonds in place is due to the net electrostatic attraction between protons and electrons of bonding species. This is akin to the force holding two magnets together. The attraction between two magnets is stronger when they are close together (a strong “bond”) and weaker when they are farther apart (a weak “bond”). It takes energy to move magnets apart—going from a strong bond to a weak bond. When magnets are allowed to come together—moving from a relatively weak to a relatively strong attraction—kinetic energy is given off, and work can be done. Thus, magnets at a distance have more potential energy than magnets in close proximity. Weak bonds have more potential chemical energy than strong bonds.
