There are some periods in the life of a child that are crucial for development and learning. During these periods if the child has favourable experiences, her development will be fostered. If in these periods experiences are unfavourable, development suffers.At times, the damage done because of unfavourable experiences may be irreversible. These periods when a child is particularly sensitive to the conditions in her environment are referred to as critical periods or sensitive periods.A critical or sensitive period is that time period in life when an environmental influence has its greatest impact on the development of the child.The 'sensitive period' in child development represents the optimal period for particular capacities to emerge in an individual.It is the period for the child to develop particular capabilities. It is the time when the brain of a child is most receptive to a certain type of stimuli.A sensitive period is one when the child is maturationally ready to acquire a skill. During this period the child must have favourable experiences which will help her to acquire the skill.If the favourable experiences come after the sensitive period is over, the child finds it difficult to learn.During this period, specific experiences affect the development of the child more than they do at other times. Such periods are sensitive for development because during these periods the child is ready to leam a particular skill.For example, a child begins to speak only when she is able to control the movements of the tongue, lips and vocal cords and the brain has developed further. That is, the child must be biologically ready to speak.Hence, the 'sensitive period' in child development represents the optimal period for particular capacities to emerge in an individual.