Welcome. You should have a look at the following sections. http://www.elevenplusexams.co.uk/schools/regions/essex-11-plusviewforum.php?f=15
The information is for current year 6 children but it should give you an idea of what to expect. Information for children in year 5 will be updated next year.
Cecil Jones College PAN has been reduced to 200 for 2014 entry, so the number of selective places is now 20 (http://www.ceciljones.net/images/letter ... 202014.pdf
St Thomas More offers 30 selective places, not 30%, but in practice normally nowhere near this number of children enter via the CSSE test (ditto CJC).
Your DS will be due to take the 11+ in 2014 for 2015 entry. Whereabouts in Essex are you?