Currently I am participating in the JET Programme which is a really weird experience because basically everyone one the JET program has just moved to Japan for the most part. I was an exception and had already been living in Japan for over two years when I started the JET program. I had learned the language in college and got a lot better at it living in the country and working in a company for my first year or so here.
I switched to teaching and worked for Interac for about 9 months in Chiba prefecture. It was a great place to live but one of the first things I realized when I started teaching is that people don't want foreigners to speak Japanese in the education world. They want you to speak English as much as possible so that not only the students get a chance to practice English but the staff also. I found this a really awkward situation because other than a few English teachers who can actually communicate in English everyone else can do a basic greeting and that is the end of it. So that would mean that I would just speak to two people on a daily basis and everyone else just simple greetings.
I understand that yes ALTs are there to be someone who people can practice with but I am going to be brutally honest here and say most students can't and even more don't want to. As much as you try to talk to them they don't care. I think the students were much better in Chiba but in Hokkaido it is just a joke.
I teach from kindergarten to high school in this tiny town in Hokkaido and I have only been teaching here for a year. I find that a lot of the kids in elementary school enjoy my class but anything over that when the students actually have to start learning grammar and such they hate it. Being an ALT is really awkward because you are a teacher but you aren't. For example once students get into middle school a Japanese teacher starts teaching them English and I can understand that. There are all sorts of things that need to be explained to these children so that they can understand a lot of the nuances of the language however. I think that Japan doesn't take advantage of bilingual foreigners in the educational realm.
When I was in Chiba I was often chastised for using to much Japanese in the class room and in the office. There was a teacher who would go from school to school helping out English teachers and she honestly got pretty angry at me because there was a younger English teacher who wasn't that great at English and I would help her understand a lot of things by speaking to her in Japanese. It made things really efficient and I think that the younger teacher really appreciated it. However the older teacher asked that I never speak to this teacher in Japanese again and in quite an angry tone. In Japan there is no use arguing with "superiors" even if they really aren't your superiors. Most of the time they will just believe they are correct and won't listen to anything you say. I have gotten to the point where when I run into this kind of problem I just apologize and continue doing the same thing I always did just not in front of that person.
When I was in Chiba I also taught two nights a week at a small English Conversation School and that was great. I made an extra 300 bucks a month or so and all of my students were really nice ladies who liked bring me snacks that they had made. It was really a pleasant experience. Some of the other teachers there spoke Japanese but not as much as I did. I was able to explain complex grammatical points and when I was asked how to say a certain word in English 9 times out of 10 I could answer instantly. My students really liked me and when I told them I was going to move to Hokkaido 3 out of 5 of my students quit. I can't say whether or not they quit because I did but when I was teaching there some of the older students complained that the other teachers weren't good at explaining things.
Some people who teach English in Japan excel because they simply because they can't speak Japanese. This is one of the main things schools and contracting organizations want you to do but if you can speak Japanese you realize how inefficient it really is. You can stand in front of the class speaking English simply and hope that people can understand you but most of the time that just won't happen. So the logical thing to do would be explain it in Japanese. Eventually in the Japanese education system this is what happens anyways. As I previously mentioned once Japanese students get into middle school they have a Japanese teacher teach them English. Of course there are good English teachers in Japan who can speak a lot of English but I would say it is almost 50 50. Some teachers can hold a conversation with you and some can barely get across what they want to say.
So learning Japanese winds up getting you no where in most cases if you are teaching in Japan. Of course outside of school you can make a lot of friends and communicate but inside of the class room if you follow the rules it does almost nothing for you. Where I am currently teaching I teach solo from really young kids to high school students and in all of these situation I use lots of Japanese. I think that if I wasn't able to speak Japanese teaching in this town would be almost impossible. However I get no special treatment no pat on the back saying good job. They just take it for granted that I studied the language for 10 years. It's been one year of teaching in this town and I have had the occasional person tell me I was doing a good job but I would be extremely happy if someone made any mention about how my language ability facilitated all of the students in this town to be able to learn.