My DS (now 4.6) is in Reception at an independent school. Prior to this he went to both state and independent pre-school (the latter being attached to his now school).
At BOTH pre-schools DS had almost entirely negative feedback on his social skills. His academic skills were never mentioned. The manager at his state pre-school told me that the independent school we had selected wouldn't accept him due to his behaviour.
DS found it hard to sit still, wasn't keen on joining practitioner led activities, preferred to play alone, was disruptive if not kept engaged. He often seemed baffled by the rules of the classroom and frequently got told off. So much so that he seemed to take scoldings as an occupational hazard.
So in September he went into Reception with me a nervous wreck. His teachers regard him very highly, claiming he is a joy to have in the room. They have highlighted some of his traits as being potential autism spectrum. With their support we met with a child psychologist who thinks he's just a bit socially immature ( being a boy, summer birthday, only child).
The teachers have taken the time to understand his ways, he is making great progress, I hardly ever get the been naughty message after school.
It has been difficult and at times saddening to watch little DS struggle to adjust, but he has and that makes me 
If he had been kept back a year I feel it would have been very detrimental to his social progress, the very element that the move would have sought to address.