Hi LG.
I've just started electronic engineering at uni, and you will probably find the first year just as boring as electronics at school is for you now.
The thing I have found it to think about these situations calmly and clearly - take emotions out of the question.
Whilst making a light out of an LED, resistor and PP3 may seem very wasteful, boring and stupid, remember that you are feeling that way because you already have a knowledge of electronics. Most of your classmates, if not all of them, will have no experience at all with electronics, and making such a simple circuit is actually really cool, exciting and interesting for them. They have not had the same chances as you. Even Mr Teacher might not have the same experience as you.
If you were in Mr Teacher's position what would you do? You could either;
Start with a basic LED, resistor, PP3 light circuit, which would help 99% of the class,
or start with Fundamentals of Quadrifilar Helix Antenna design, which would be interesting to 1% of the class, but would make sure everyone else never wants to do electronics again.
Which would you chose?
Remember, teachers have very hard jobs. In the UK, the first role of a teacher is not even to teach. It is to ensure the safety and well-being of their students. So before Mr Teacher can even think about designing a circuit, think of all the hard work he has to put into ensuring all students have a safe environment, come in on time, sit down and behave, take the register, paperwork, lesson planning, etc etc... There may have been other reasons why Mr Teacher didn't want you to be smoothing the edges. Perhaps he wasn't allowed to let students use files in that lesson for health and safety reasons? It may seem silly, but again, not all children have had the same opportunities as you, and may not know how to use a file properly. This is something he could loose his job for. Definitely not an overreaction.
There are situations in life where taking too long with something, or doing something you were not meant to can be very serious. Even life threatening.
From what I have seen, you have a great knowledge of electronics, and the that regard, I admire you for being interested in something, learning about it, and holding onto that knowledge. But with great knowledge comes great responsibility.
I have no doubts you will coast through GCSE electronics. Even A-level electronics. But your teacher is still your teacher, you need to have respect for your teacher no matter what.
Take care, enjoy your school days whilst they last. (geeze, I never thought I'd be saying that so soon!
)
SS