Abigail, aged eight weeks, had happily encountered many strangers who had picked her up and cuddled and played with her. But the moment Angelina took her into her arms she began to scream inconsolably. Returned to her mother she calmed down but, faced with Angelina again, the screams intensified once more; this baby was furiously angry. As her mother calmed her once more, she noticed Angalina's long, dangling gold earrings. After these were removed, Abigail returned to her arms and cooed with pleasure.

The incident brings to mind Montessori's description of a child enraged by his mother holding her coat over her arm. Her explanation was that the child was distressed because its sense of order was being violated.

Studies of very young babies have shown that the human face bent low over the crib within their limited field of vision is the most important visual stimulus in the first weeks of life. Babies quickly learn the pattern of a face to the point where they will even respond positively to a picture of one, although the real thing always produces readier first smiles. However, if something is added or taken away from the pattern of the face babies often become upset. Men with beards, aunts in sunglasses, a mother's radical new hairstyle, even a pair of earrings, can destroy this early sense of order and provoke screams of anguish.

Writing in The Secret of Childhood, Montessori mentions "the sad and violent reactions of children when their vital activities are checked by external obstacles."

These reactions, described as caprice, wilfulness, whims or tantrums, are popularly thought to be without real cause, though Montessorians would say that what they are really revealing is an understandable inner frustration.

One of the most practical and easy to understand Montessori principles is that of sensitive periods. Sensitive periods are transient stages in the child's early life when he or she is "tuned in" to certain aspects of the environment. There is so much stimulation surrounding the child that he needs an inbuilt mechanism to make sure he acquires the most basic skills and abilities. With language development, for instance, the baby is attuned to the human voice above other sounds; he does not lie in bed making telephone or washing machine noises, but tries out the sounds of speech. The child is in the sensitive period for language, this is the time when he needs to be talked to and the best possible stimulation comes from one-to-one conversations with an interested and lively carer.

Montessori designed a nursery school environment and curriculum which would feed these different stages of interest in children's development. Once parents know what the major sensitive periods are and what levels of ability are normal for a child of two years of age, for example, they can provide prepared environments at home. The idea is not to set up "school" at home, simply to key into what children are drawn to at particular times and to provide activities and settings which feed and stimulate them. There is no need for the adult to "teach" because the child will absorb impressions naturally.