Welcome to the forum. Have a look here,
http://www.readingschool.reading.sch.uk ... 3plusExams
http://www.readingschool.reading.sch.uk ... ions#Areas
Just checked and the "designated area" of postcodes does apply to 13+.
Boys take the exam in January of year 8 for September entry into year 9.
One source told me it was about fifty boys chasing the twelve places.
My DS1 is in year 9 and he says the three new boys in his form group have settled in well, they all seem to have something in common however tenuous
mine worked out that he had been at the same nursery school as one of the new boys. A team mate of DS1 from club rugby started in year 9 this September and chatting to his dad his son is enjoying the new challenge at Reading school.
Some issues arise in specific subjects but they can be caught up or dropped at GCSE choice time.
I think you have nothing to lose and a lot to gain, so go for it.