Admission of my child to L.K.G.

My daughter is already in the prestigious Sacred Heart Convent School and an 'O' grader throuhout - she is in std. IV right now. I, myself am an educationist and my husband is a second officer in the Merchant Navy , in short , both of us are well educated. So I was pretty confident that my son too would get admission in the same school. Moreso, it was one of the basic needs for me since in the absence of my hubby , it becomes very ough on me to run between two schools , not to mention various other chores. Therefore it was a shock when the respected Sister refused admission to my son and would not listen to any of my pleas , this despite the fact that many other people were flaunting late admissions in the same class on the basis of jacks and what not. I kept on wondering for many days and I still wonder what exactly is the criterion that these prestigious schools follow to select students for classes which are bursting at their seams with a ratio of almost >60 students : 1 teacher and where sometimes the teacher doen't know what to answer if you ask about your child's shortcomings / merits ; they have a standard answer that everything is fine . In retrospect , I think any good English medium school would be fine for me which has a reasonable student teacher ratio , where my child would not be just another cute face and where the presence of an intelligent sibling would ensure that my other child would get admission also.
I, myself being a teacher can very well appreciate the anxieties of all those working mothers/parents who have to rush about to make each day a success and I must say that I was very much disappointed when a good school and no doubt a good Sister failed to understand and appreciate the same.