Why punishments and especially rewards re counterproductive
Montessori pointed out that the classic school desk is the means of deliberately and artificially paralysing children so that they can be managed and treated as things in large groups. She continued;
"The rewards and punishments are, to speak frankly, the desk of the soul, that is, a means of enslaving a child's spirit, and better suited to provoke rather than to prevent deformities. Actually, rewards and punishments are employed to compel children to conform to the laws of the world rather than to those of God. Too often a teacher commands because he is strong and expects a child to obey because he is weak. Instead of acting in this way, an adult should show himself to a child as a loving and enlightened guide assisting him along the way leading to the kingdom of heaven. Anyone who uses his talents can be exalted, and everyone can receive a reward , whether he has many talents or only a poor single one.
But in school there is only one prize for all of those "of good will" who enter the race, a fact that generates pride, envy, and rivalries instead of that thrill coming from effort, humility and love which all can experience... One day a child will surely ask himself if the prizes won at school were not rather obstacles on the way to eternal life.....No one who has ever done anything really great or successful has ever done it simply because he was attracted by what we call a "reward" or by the fear of what we call a "punishment". If an army of giants were to wage a war for no other reason than to win promotions, stripes, or medals , or simply to avoid being shot, against a band of pygmies, inflamed with a love for their country, the latter would certainly obtain the victory...Every victory and every advance in human progress comes from some inner compulsion. A young student can become a great teacher or doctor if he is driven on by an interest in his vocation; but if he is motivated solely by the hope of a legacy or .. some external advantage , he will never become a real teacher or doctor... If a young man must be punished or rewarded by his school or family to make him study for his degree, it would be better for him not to receive it at all. Everyone has a special inclination or special secret, hidden vocation. It may be modest, but it is certainly useful. An award can divert such a calling and turn one's head to the loss of one' s true vocation"
Maria Montessori "The Discovery of the Child" pp15 -18)
(My experiences as a teacher and parent led me to believe this before I read this eloquent explanation of the phenomenon by Maria Montessori.)