I would like to know about Montessori and socialisation. Did Montessori write some specific chapter or book about it?

Maria Montessori wrote specifically about the socialisation process in two chapters of The Absorbent Mind, chapter XXII:  Social Development and Chapter XXIII:  Cohesion in the Social Unit.

Since so much of Montessori’s work for children under six focuses on individual development the question, “But what about social development?” gets asked many times.  We believe strongly that any social fabric is only as strong as its individual members. Children in the 6-9 age group are quite naturally interested in forming clubs, groups and understanding the rules by which groups function. They practice group membership and the clubs often change frequently. But the success of endeavours such as Scouts supports the interest in working/playing in groups.  Montessori mentions in the chapter on social development the elements that support social development, namely large groups (ideally around 35 children) mixed age groups (2.5 – 6+), everyday living together which creates many occasions for social activities, specific activities called the grace and courtesy (G & C) activities.  These G & C activities give children information about cultural expectations in which they are living and the knowledge of how to carry out these various expectations.

Quoting from The Absorbent Mind, “There is among children an evident sense of community. This rests on the noblest feelings and creates unity in the group. These examples are enough to teach us that under conditions in which the emotional life reaches a high level, and the children’s personalities are normalized, a kind of attraction makes itself felt.”

Laughing group of children in a Montessori classroom