I am currently an ALT in Takayama City, Gifu through the JET program.
I started in January 2013, and worked in 1 Junior High and 2 Elementary schools. My schools were fairly large. My Junior High had about 400 students, and my main elementary school had 600. My other elementary school was super tiny and had only 18 students in the entire school. Because of the size, my elementary schools basically planned all the lessons, and I created materials and then followed their plan in class.
Well, things change. In August 2013, I switched to much smaller schools. I now have one Junior High with only 70 students. And I have 3 elementary schools of 150, 200, and 400 students. In the smaller 2 elementary schools I teach all grades, and in the other school, I teach 4th, 5th, and 6th. My position is much more focused on elementary school teaching now. Also, I am in the only English teacher in my elementary schools, so I do all the planning, material creating, and executing in class.
The following are all my lesson plans I've written for use in my 3 elementary schools. For all of my classes, I have 4 different levels that I write for: 6th, 5th, 4th and 3rd, and 2nd and 1st. 5th and 6th are the only grades that have a specific curriculum to follow. The other grades are simply at the whim of the ALT. The younger grades tend to have way more games, and repetition.
Most of the ideas I used for these lessons came from Englipedia, other Takayama ALTs and teachers, the recommended lesson plans, plans from my predecessor, the Team Teaching Pizza book, and random other websites. Sometimes I get an original idea and try it out.
For each of these lessons, I will write out the plans almost a week in advance and discuss the upcoming class with the homeroom teachers. I will ask for any help I need from them, and get their OK on the plan before executing in class. After teaching the classes for long enough, you'll get a sense for the student's limits of English and study, but it's always good to talk with the teacher and explain anything you might think is challenging, or possibly difficult for the students.
In the official declaration of the Ministry of Education, in elementary school, only 5年生 and 6年生 are required to learn English. They must have 35 hours throughout the entire year. And this is the current text book the students are issued. Hi Friends 1 and 2 - 平成24年4月 version. You can buy a copy of the textbook on Amazon for 95円. :) All my lesson plans and flash cards are based on this book, and occasionally I'll actually do an activity directly from the book. I use the text book for a general layout of all my lessons throughout the year, but almost all the the instruction is in class teaching directly.
One really nice thing about Hi Friends is that the Data CD contains full PDF versions of each book. Almost all the artwork in the book is in Vector format, which is AMAZING. Most of the flashcards I've made for my classes has been from rasterizing those PDFs is various sizes. It produces lossless perfect images. But when the book doesn't provide good flash cards, I usually resort to Google Image Search, and try to find large photos aren't terribly quality.
This page now exists here: ALT Materials & Lesson Plans