Initially, the child will try to understand the new surroundings, but once it known the school routine, the place of school, it immediately realizes that it would be separated from mother and rest of family for sometime. Hence the desperate cries and clinging tightly before they can be dropped at school.
It is hard for the parents to leave such crying frightened children but that's they way they learn to handle separation as they start growing. Schools have a settling in period wherein the little ones are left for a short period with the mother or father being slowly weaned off for longer periods. This is handled better when compared to a child that is put into kinder garden suddenly for the full session.
If the children are from a joint family children will easily adjust to a different atmosphere. Also if the child has a brother or sister there will be difference in child' s behaviour at school. The present nuclear set up is behind this attitude of the children. They are grown as autocrats in their home. Father and mother always adjust for the child and provide everything demanded. All these cause the child to keep away from others.
Another reason for children crying is that in a classroom they cease to be the centre of attraction. In a class of 20, 30, 40 young kids, a child has to vie for the teacher's attention. It brings in a lot of insecurities and a child has no other way than to cry, to express his discomfort at the situation.
"A love affair with knowledge will never end in heartbreak." -Michael Garrett Marino
Service to mankind is service to God.