"What is there in the life of each of us that requires our full attention at a particular age, that is vital for that age or for coming ages and cannot be postponed?" This is the question Caleb Gattegno poses in his age-related trilogy The Universe of Babies, Of Boys and Girls, and The Adolescent and His Will. In this book, Gattegno makes proposals for the study of children of elementary school age, and provides some answers to questions helpful in improving as a teacher of boys and girls in all school subjects.