While I can appreciate that most kids make friends easily, from experience, it still can cause more harm than good by forcing children into situations to continually make new friends and break the bond they have with their current close friends.
My daughter was with the same group of friends for junior and senior kindergarten, but then in grade 1, she was placed in a class where she only had one male friend she new from the year before. My very energetic, positive little girl who was extremely enthusiastic about learning became very quiet and introverted. As a result, the other children in her new class who had been together for years began to pick on her, and she became desperately attached to the one little boy she knew because he would stick up for her.
We tried to wait it out, give her time and encouragement to make new friends, however by the time we said enough is enough, the school said it was too late in the school year.
Children need comfort and to develop trust with other people. It is the same principal of needing stability and consistency that experts say children suffer from a lack of when they frequently change schools, but worse because they are dangling the old life in front of her.
Please also bear in mind that my daughter was always very ahead of the game, and her former teachers would praise her and pointed that both academically and socially she shined. A few months into the school year last year, the teacher started sending notes saying that she was showing no interest in completing school work or participating. While I don't want to place the blame entirely on her social situation, it is important to note that her home life has been very stable. Mum and Dad still working the same jobs, she was still participating in the same extra curricular activities and there was no excessive fighting with her siblings.
She also remained very social at her dance studio, maintaining some of her old, and making new friends there just fine.
We just brought her in to school today to find that this year she is again with a bunch of different kids, and her one best friend is now back in the class with all their old buddies and she is even more alone. Watching her stand at the school wall with her new class, isolated and alone, while all of her old friends laughed and joked ten feet away left both her and I in tears. We will be going to the school tomorrow to see what can be done.