I'll tell you my experience. Bear in mind it is only my experience with my DS...
My son started a new nursery at the age of 2.9 yrs. For the next 6 months or so he was a bit unsettled. He seemed to enjoy going to nursery and didn't mind me leaving, so it wasn't the usual settling in traumas. However, the nursery became increasingly worried and to be honest I think exasperated by his behaviour. In relation to the stuff you mentioned:
Empathy/ perception of others' feelings - DS wasn't great. He was/is a highly verbal child, so could say what behaviour he klnew was wrong and how he should act etc, but was completely unable to put it into practice.
impulsiveness - he was completely impulsive and would grab for things, sancth toys, push children out of the way. He found sitting still /waiting his turn virtually impossible.
knowledge of whether something was 'naughty' etc - completely lacking. Again, he could verbalise it all beautifully after the event, but had no self control often pushed / hit/ bit other children out of frustration or to get his own way
perception of danger - non existent. Would run out in road or climb a high tree etc
energy levels etc - would basically run around like a nutter until he ws completely burnt out. No ability to settle at quite play while at nursery 9although was fine at home!)
concentration - again, very good at home (could do jigsaws or play with lego alone for extended periods, but at nursery he flitted from one thing to another and never settled.
interacting with other kids - quite poor. Bossy, aggressive, didn't want to play with them or even alongside them a lot of times
It;s worth mentioning that as well as being a very bright, verbal child, my son is physically very tall and strong for his age. He seemed (and still does) to need a lot more physical exercise than many other kids his age. His height also made minor scuffles more serious, as the pushing and shoving that can go on between 2 and 3 yr olds was made worse by the fact that a push or shove from him against a smaller child always had worse consequences!
After 6 months the nursery started talking about calling in SENCO. I was upset, but so worn down by constantly being told at pick up time that he had bitten someone / disrupted an activity etc that i thought maybe it was appropriate.
There was a small improvement in his behaviour just before the end of term and they decided to hold off on calling SENCO until the following term.
Anyway, to cut a long story short - his behaviour has slowly improved of it's own accord in the last few months. he is now 3.7 yrs old and behaving much, much better. The biggest and most noticeable improvement has been in his ability to get on with other children, play together etc. I really believe this is developmental. He has, to put it simply, started to grow up.
He has also started a new nursery who were horrified to learn that his old nursery had considered calling in SENCO for such a young child without very good reason. The new nursery teacher thinks that all the behaviour we described was completely normal, developmentally, for some children at that age and that labelling a small child as 'difficult' at such an early age was utterly wrong. Interesting. The staff there were also unimpressed with some of the 'strategies' his old nursery employed in order to get DS to behave - basically, lots of 'naughty corner' type action. They are much more concerned with heaping praise on young children for good behaviour and dealing quickly and firmly with bad behaviour - but not dragging it out with prolonged periods of withdrawing the child. This attitude has had a fantastic affect on ym son, and we are using it at home, too. He positively shines at nursery now - he adores praise and appealing to this love of praise is working wonders with him.
In retrospect, it makes me very sad and a little angry that his old nursery didn't seem to follow any of the good sense written in virtually all literature on child development. If they had've, they never would've thought of calling SENCO. Thank God they didn't!
Sorry - this is an essay, but what I mean to say in a nutshell is - think carefully about all this.