My wife read this thread and asked me to respond as I have been mainly involved for his preparation for the 7+ exams.
We chose for our son WUS, although he had admission to all the leading schools (including Latymer and Wetherby plus the usual 3). He came from a State School and had no outside tutoring. However, parental guidance and work at home was necessary. We do not believe it is a good idea not to do so.
Our son was very good at Maths. So is your son. In that case, you should have no worry at all. We believe (but we cannot be sure) that he scored perfect scores in Maths in all the tests, and that carried him through. He is bi-lingual, English is not his mother tongue, and he is not good with the English idiom. But that did not matter in any school, because of his Maths and VR and NVR – all of which (we think) he scored perfect scores.
From Reception, he had been to Science Museum (perhaps 30 times, if not more), the Natural History Museum, the Greenwich Observatory. I (an occasional volunteer teacher in Maths up to A level) realized he loved numbers, and started discussing with him simple problems. He graduated to fractions and decimals by the end of Year 1 – when I stopped, as I realized he was bored in his State school. We did nothing in Year 2. Around the October midterms (before the January exams) we bought the Bonds books (and CGP books); we did the age 6, 7 and also year 8 with him. Maths was no problem, but he had serious comprehension ( or at least writing good English) problem. We got him to write 3 paras every week on anything interesting that had happened – beginning, middle and end paras maximum 15 sentences in all). There are serious concentration issues with a 6 year old boy – you can train him for only that long. Also, during the week he swam twice, played football, went to Spanish class (his mother tongue), had Chess club, and also had normal school HW – so, these extra work was reserved for the weekends.
I should add – get you son to read, or read out to him some (not all !) books from the CC list for 7year olds. He will develop vocabulary, which you can track in a notebook for new and nice words – to be revised before the exam.
Any of the best schools will develop any latent talents the student may have – but the student must have the talent in the first place. If your son is good in Maths, you may relax a bit on the other topics – they will realize his potential.
A final word – my wife read quite a few negative comments on the Master in various threads on WUS. Do not believe these. She is terrific! She has state school background, and has taught in both State and the Private sector, and she is warm, affectionate towards the students, and knows each of them well. The people who were disappointed with the Open Day forget that three hundred children descend with their parents in what is a small school (half the size of CC, which has also the resources of St Paul’s). It is normal for that to be chaotic – but mix with the teachers, and see them come alive when they talk of their students; observe the boards in the Maths room, and understand how much advanced for their age these students are being taught, and they (the students) love it!
Best wishes.