Nobody knows how many children will sit this September, but probably a bit more than last year. Last year, ca. 2500 boys sat SET for Sutton grammar schools. Wallington boys' passed over 840 after SET and they did not have the second stage, so all of those were eligible to put Walligton boys' on their CAF. SGS and Wilson's probably passed similar, or slightly higher, numbers to Stage 2 each and after stage 2 roughly 550 children were deemed eligible to apply for each of these schools and put them on their CAF. Not everyone who passed Stage 2 SGS passed Stage 2 Wilson's and vice versa. The total number of places in boys' grammar schools in Sutton was 450.
I don't know how many sat Tiffin Boys'.
More precise data for 20016 exams will be available in Sutton's Secondary Schools Transfers 2017 booklet when it is published - I think in early September. In the meantime, here is the link to the 2016 edition of the booklet, where you will find numbers sitting the test in 2015, so it will give you some idea. https://www.sutton.gov.uk/downloads/fil ... oklet_2016