Light Yagami/Harry Potter
That was only the first of the problems Light had to face in KG. Some problems, like making sure Dudley was properly taught the basics, were new to him. Others, like integrating into the class and not getting pointed at and bullied for his intelligence, were old. Light was used to them.
Another new problem, something that Light noticed after he started correcting Dudley's learning curve, was the cultural classroom differences between Japan and Britain. In Japan, people wait until they are called on to answer a question. Standing out too much in any way, shape or form, was not tolerated. Initiative was appreciated only as long as it was kept on the down low. As a result, within the first three months of classes, Light was firmly in the category of 'that weird introverted kid'. High on the easy-to-bully ladder and low on the friendship ladder. The first, Light took care of expediently and with generous help from Dudley. The later, Light didn't really care about. Not at this juncture.
Light was polite when addressed to by adults, short and to the point when talking to kids and made sure to keep out of sight when throwing down a bully using an Ippon Seoi Nage. The NPA physical training was really good for Light, in hindsight. Perhaps he should have relied less on the Death Note and taken more Judo classes for self defense.