I was a a physics and chemistry teacher at Mkwawa High School in Iringa,Tanzania from July 1965 to April 1967. One of my students was Erasto Mpemba. One of the subjects in the A level physics syllabus was Newton’s Law of Cooling. The law basically states that the rate of cooling of a hot body is proportional to the difference between the temperature of the hot body and its surrounding temperature. According do the law, it should not matter at which temperature a hot body starts to cool since all such bodies should go through the same temperature trajectory.

    However, Erasto was able to show that a warmer body cools or freezes faster than a cooler one does. When Erasto brought this to my notice, I at first did not believe it. Urged on by the class and Erasto himself, we did the experiment and, lo and behold, he was right: a warmer body does freeze faster than a colder body. I was at least honest enough to admit that I could give no explanation. This happened quite early on in my teaching period in Mkwawa High School, so my aura as a teacher who could not fail suffered as a result. Erasto Mpemba was a very enthusiastic student, and I am glad to say he passed the A level exams.

     I saw him once later in Dar es Salaam, and he told me that he had a good government job, which was what most students in those days were aiming for. In 1967, I went to the MBA course at INSEAD in  Fontainebleau, France. A local French business publication cited the case of the Mpemba Effect as an example of how one should not always trust the received wisdom. One of our professors on the course used this article as an example and to the astonishment of the other students, I was able to reveal that I was the teacher who did not (initially) believe Mpemba! Moral of this story: be careful to believe what others say is the truth.

Brooks Goddard adds that Eugene told Dar 05 of this event, and you can Google "Mpemba Effect" and find that it has its own entry on Wikipedia.