I understand your frustration, but in this paticular private school his teacher is most likely right. Many private schools excell more rapidly than do their public counterparts. Part of this may be contributed to the fact that they tend to have smaller classes and that they will keep a child back for "immaturity".

I had a private school just "suggest" that my granddaughter be removed and placed into a public school where she would do better because the students there would be "more like her with similar backgrounds". She is from a low earning family. Her mother was told that the public school would be better suited to deal with her behavior.

I worked at a public school close to this same private school for many years. Until this happened (right after Christmas) I didn't realize why we had so many transfers to our public school at this time of year. Our children transferred in were either behavior problems or had problems learning. These children were mostly from this same private school. The private school is telling parents that they should move their children because they can get the help they need there. They are transferred in the midst of the year when schools do not have time to evaluate the need and must start over the next year anyway.

The state where I previously worked in kindergarten we were not allowed to keep a child back due to immaturity. I'm not taking sides on this issue because there are many pros and cons to both sides.

You speak of your son you say,  He is ... somehow spoiled and gets angry easily if things are not done his way and would complain that things are not fair to him. He also has a hard time obeying and following instructions, if he is happy and wants to do something he will follow and obey but if he does not want to do something he will just whine and will not do what you asked."

You don't mention if he is a first or only child. Many times when one of these are true "we" as parents tend to dote over the child and he/she is used to getting what he/she wants when wanted. It is very important to teach patience and be consistant in praises and punishment. When there is something that he wants to do you might have him take a minute to do something else you want him to do before giving in to his wishes. Make sure to explain that you will do what he wants as soon as he is finished with what you asked of him. Make absolutely sure that you follow through on your end of the deal.

I have found both in my professional experience as well as with my children at home that time outs using the child's as as a guide for the time removed from social interactions works well.  

As far as to move up or stay back, I say go with your inner gut. You might find public school to be a better fit for your son since he wouldn't know the other students and no one would know he was held back.

Thanks! My son is indeed the firstborn :-) and we are trying with timeouts and not giving up, i plan to do more educative playing at home with his little sister in the hopes that he will improve, but  guess me as a parent have to improve too.

YOU REALLY SHOULD OFF ON HIM OR HER. OMG i cant believe they told him that

I am going to say this in the hopes that you'll understand my typing...if I were you, I wouldn't keep your son back! Boys are usually more immature that girls, that's just the way it's always been!  Sometimes we'll get lucky and find a boy that happens to be mature but that's unlikely!!  I can tell you one thing, if he needs to be kept back, let it be in 1st grade when you'll know that he needs help for academic reasons and not social reasons.  I am a homeschooler of 5 children so yes I do know what I'm talking about and guess what...I kept my son back in 1st grade because he wasn't able to move up after leaving public school!!  Good luck with whatever your decision happens to be.

Kindergarten is not mandatory. It is a first introduction to the classroom setting and structured learning for most children. Mostly, it is a time when children are presented with challenges that, to them and the parent, are monumental. Do we remember our own apprehension on our first day of Kindergarten? Emotional readiness is best achieved by doing what you, the expert on your child, feels is best. Feeling is emotion, not a clinical study of a cross section of the five year old population in a particular school. If you are told that your five year old is not ready for Kindergarten, it is either a confirmation of what you already feel or the need for someone in authority to justify their expert status. There is nothing harmful in trying something out for a few weeks, then withdrawing until a later date if it doesn't work out. There is much to be said, also, for the "sink or swim" approach. The attached article from EDUCATION.COM addresses the issue of emotional readiness for school in a fresh way, but having already been through the separation anxiety of preschool, you are probably more of an expert than you know. Certainly more than anyone else as regards your own child. Don't let yourself be bullied!