If the teacher understands that they are talking about, that is really important, but I don't think that automatically makes them a good teacher.
In my opinion a really good teacher is someone who is passionate about both learning and teaching. They are excited about what they are teaching, which is infectious and in turn makes the students excited and engaged. They are good at communicating. A really good teacher is someone who understands that you might need to explain the same concept different ways to different students because there are different learning styles. While one student may be able to hear an explanation, another student may need that explanation worded differently while another student may need a visual aid to understand the point a teacher is trying to make. A great teacher will be able to teach across all learning spectrums or be able to explain the same concept a number of different ways until something clicks with the student. And finally, a teacher needs to be knowledgeable on the subject they are teaching.
If you end up with a teacher who is not excited, cannot communicate or does not know what they are talking about it can make learning an incredibly difficult and frustrating experience.
If you are in an instructor position, I would strongly encourage you to do research on learning types and related teaching methods. There is nothing more frustrating than being a student and asking for help and having your instructor be unable to communicate with you in a way that you understand.
For example, this evening in Aikijutsu class we were practicing shomen uchi irimi nage and one of the assistant instructors made the comment that I was doing certain parts of the technique wrong. (Go figure, its the 20 year throw...) They then showed me how to correctly perform the technique on the other assistant instructor. While I do pick things up visually I am a much stronger at learning kinesthetically. (which is to say I have to do it to get it) I asked the instructors to walk me through the technique as I was doing it on them. Instead they proceeded to show me the technique on each other several more times and explain in great depth the concept and workings behind the technique. I understand how the technique works, but if I cannot feel where I am doing the technique wrong or right as I am actually performing the technique, all that knowledge is useless to me. I asked them again to please allow me to do the technique and walk me through it as I was doing it. The instructor who had initially made the comment I was having problems continued to say "No, watch, THIS is how it works," while still doing the technique on the other instructor. After a good 5 to 10 minutes of having both assistant instructors try to help me and another student chime in and I became so frustrated I gave up and just went back to trying to figure it out with my partner.
This is NOT ok! If you are a teacher or instructor in any field, I IMPLORE YOU, on my knees, to please research learning styles and teaching methods for the sake of your students. PLEASE.
For Martial Arts instructors specifically, Sensei Nick has recommended Martial Arts Instruction. This is the next to read on my list.
Next post I will post a bit about learning types and related material. Till then, keep it cool everyone.
~ Samurai Girl Sahara