The curriculum is formulated with an underlying structure.  In this way, the needs of various children are met successfully.  It provides an atmosphere for developing the child's self-concept.  The child becomes aware that they are a special individual and worth liking.
The younger and older children are encouraged to play together.  In this way, the younger ones learn from the older and their presence leads the older ones to help them. It is also realized that the little ones need quite and leisure and closer contact with the teacher part of the time.
The older children need opportunities for intellectual experiments which would be hampered by the constant presence of the younger ones.  Thus we do separate by age groups, getting together part of the time for similar activities.