I read this book for the first time in highschool years ago and re-read it again since.
What most impressed me was the author's ability to set up atmosphere in the novel. I still to this day, after years between readings remember images I formed while reading the novel. Grass between the toes, the nuclear wastes, the way the children formed telepathic images etc...
One thing that I remember clearly is how the novel was like a breath of fresh air, clean and smooth. There are no frilly edges and there is no attempt by the author to make the book flashy. This makes the book pure and adds to the impact of the story.
As an overview, there are a group of children who are living in Eastern Canada after some type of holocaust (this is never much of a point in the book... no one has memories of it). Their society is strongly anti-mutant with a very strict set of rules as to what is "normal" and what isn't. All of this children are normal looking but are telepathic and form a click of just a small number.
The book is their story of growing up and existing in this paranoid and highly dogmatic society without being discovered and banished or killed.
A definite classic in Science Fiction circles.