Different language, faith(religion), caste. Similar socio-economic background, residential neighbourhood, age and school. Do they divide or unite? Fortunately the latter in most cases I have encountered over several years of teaching and counselling children from low income families. Although the children are very conscious of the differences. And highlight them without hesitating to be direct when they deem necessary!
But, gender identification and stereotyping builds in early in the kids and increases as they enter teenage. I discovered this with Srikant, a class V government school student who refused to sit beside any of the girls despite insufficient chairs among the boys. Similarly, Kumar of class VII said "Cleaning is a girl’s duty!" I admonished both of them severely and entrusted the latter with the responsibility clearing the trash after a birthday celebration. At least he didn’t protest openly. The girls were not surprised at their attitude but resolved not to accept such remarks now or in future.
Shashikala, another class VII government school kid was a welcome exception when she successfully separated two of her male classmates from coming to blows over a trivial issue. And some of them (like Saraswati and Satish from Gurupanpalya or Amala, Ashwin and Ajit from Byrasandra) harbour fraternal feelings towards each other even when they are biologically unrelated. This is especially the case when the children have jointly organized events or are involved in community activities like tutoring or mentoring younger kids in their neighbourhood.
However, regrouping based on gender is common except in some cases (as above). And those children (like Mubarak) who ignore this are often jeered at (by seemingly playful boys like Chetan and Pavan) rather than cheered. Further, the segregated seating arrangement in schools right from class IV seems to promote it.
To foster healthy relationships, I have often deliberately made boys and girls sit together, interact with each other and share work and fun as much as possible. This has sometimes resulted in weak protests by older children and some teachers but I have ignored and overcome them successfully. My greatest encouragement came from one of my oldest students Ganesh, now a community health worker who married Kalai, a government school teacher and another of my initial set of students. He told me sometime back "Akka, learning about gender equality from you is what makes me help her with housework!"