Cortina,
The reassuring thing about your son is that he is "holding his own".
It is all about individuals, as mrz says, though I hope she realises that as a matter of simple arithmetic, if you made a list of all the struggling children that all teachers in the country come across, there would be more summer-borns on that list than autumn borns.
When you read the awful statistics, you have to remember that the children who are affected throughout their education are likely to be the ones who combine their July/August birthday with some other factor personal to them that creates a bit of a "double whammy" (such as, for instance, being immature compared with other children born in the same month as them, or - alternatively - being mature enough to realise they are behind and "switching off" from education due to lack of classroom support).
It doesn't sound as though these additional factors apply, so with your support and school's support, I'm sure he will find his natural level within the next few years.
We have deferred our son for a year, he will start reception at 5.0 in the state system. It has transformed his life chances. This is not just my view, but the view of the SENCO, headteacher, paediatrician and speech therapist.
He was one of the "Classic" types of children for whom either an autumn birthday or year-deferral is crucial: late August birthday PLUS some special needs that meant he was not reaching the social communiation milestones for a 3 year old - let alone a 4 year old! - until the term after he had been due to start reception. Once the special needs were being addressed, and he was ready to start practising communication skills, it was desperately important to place him in a cohort where there were a reasonable number of peers at the same social communication level (ie the year below his official year) and he flew...... had we been forced to put him into reception in his "official" year, his best hope would have been to retreat into academia and be protected by the most socially mature children of the class.
I think that year-deferral should always be allowed if a developmental paediatrician recommends it.