Gray, P. (2013). Free to learn: Why unleashing the instinct to play will make our children happier, more self-reliant, and better students for life. Basic Books.
Trích dẫn kiểu Chicago (xuất bản lần thứ 7)Gray, Peter. Free to Learn: Why Unleashing the Instinct to Play Will Make Our Children Happier, More Self-reliant, and Better Students for Life. New York: Basic Books, 2013.
Trích dẫn kiểu MLA (xuất bản lần thứ 8)Gray, Peter. Free to Learn: Why Unleashing the Instinct to Play Will Make Our Children Happier, More Self-reliant, and Better Students for Life. Basic Books, 2013.
Cảnh báo: Các trích dẫn này có thể không phải lúc nào cũng chính xác 100%.