My 3YO is 4 in March so starts school next September. She's a delightful child. Sweet and plays nicely on the whole with others. I think she's really quite smart (can easily do a 50pc jigsaw without assistance, can do quite complicated lego, can easily count large numbers of objects, can sound simple words out etc IF she's in the mood lol) her vocabulary is pretty good and she uses long sentences and complex words in the right context (eg she told me she was embarrassed the other day) and has multiple books and nursery rhymes memorised. Gross motor skills are great, riding a pedal bike no stabilisers since just turned 3..her fine motor skills are equally good, writes her own name first and second and draws some pretty nice pictures.
Now the things that might be a problem... She was having speech therapy for articulation issues. She has now been discharged as she's come on leaps and bounds. Even Alexa can now understand her..hurray. linked with this she's waiting for ENT due to glue ear and slight hearing loss. Also nursery have decided to tell me that she doesn't concentrate on things as much as they'd like. She often struggles to take it in turn when playing group games apparently (I have personally found that she's actually very good with this, better than her 6YO cousin actually so I dunno..) They also said that she basically has zero concentration for anything she doesn't want to do and if they ever try and engage her eg to do small group work eg phonics or her talking games she will just mess about or refuse to answer them or keep asking her go go and play instead. However they acklowledge (as I do) that she can concentrate for ages on something she's interested in eg drawing. I must say I've noticed exactly the same thing and although I find it frustrating sometimes I considered it within the normal rhelms for a 3YO. It can be quite extreme though. Eg she never seemed to like me singing to her even as a small baby and I never though she was taking it in but now she'll come out with perfect renditions of rhymes we haven't even sung for several months. Also we play pairs quite a bit and she'll seem not to be paying the blindest bit of attention and fidgeting etc but then she'll somehow get a whole bunch of pairs 
I tried to talk to her keyworker but she gave me massive mixed messages coz in one breath she seems a tad worried but in the next breath when I echo that concern she says 'oh well she is only 3...' I think a lot of the reason she acts like this is confidence and avoidance. I think she's also quite hyperaware and even as her mum I have to remind myself that she notices more than she lets on. Has anyone had a similar child? What helped? Did they mature and do ok at school in the end? My gut tells me she's fine and I'm definitely not that worried about an underlying dx eg ASD/ADHD. I just want to support her though and don't know what, if anything, I need to do. Thanks xx