To appreciate the concept of environment and its subtle effects, it is useful to consider a metaphor. In 1991, Walberg used Tolstoy's War and Peace to refer to the strength of an army as the product of its mass and that unknown X, or the spirit of the army. Observable inputs like the number of combatants, guns and so on are insufficient: the esprit de corps is critical in determining outcomes. So it is in human environments like classrooms. Without a consideration of the crucial role of the psychosocial environment of classrooms, educational productivity cannot be optimised.