The Grammar Lab, by Kenna Bourke, published by Oxford University Press, is a grammar practice book aimed at children aged 9-12, with interesting content and exercises, appealing characters, and stunning illustrations and presentation.
It consists of three books written completely in English, covering basic grammar points: how to use nouns, verbs, prepositions, etc.
I have been using this series with Japanese junior and senior high school students. The grammar points are not new to them, but the books provide extensive practice and lots of examples of how to use language naturally. The fact that students already understand the content makes it easier for them to deal with the slightly difficult vocabulary and instructions.
I use The Grammar Lab as a homework supplement to regular classes, and find that with approximately 45 sections (37 units and 9 revision sections), one book is good for a year of classes. The production values on this series really are superb, and I really enjoy the illustrations and storylines/jokes. They do a great job of bringing grammar to life and making the drills interesting.
My only complaint with the series is with the Teacher's Books (I bought the first one), which are only 40 pages long, 30 of which consist of answers to the questions in the Student's Book, and the other 10 which consist mainly of introductions to the characters featured. This is really not worth 1,400 yen nor does it deserve to be called a teacher's book. I was expecting a lot more in terms of supplementary activities, ideas for using the text, and advice, and was very disappointed with this.
The Student Books are currently available on Amazon Japan for just over 2,000 yen. This is slightly expensive for a homework/supplementary book, but for keen students who need extra practice at using junior high school grammar in practical ways, they are very helpful, and provide an easy way to incorporate grammar practice/drills into conversation classes.