He will only have to write 1 exam.....held at the first choice school you put on your Consortium application form.
the herschel link to their admissions page is as below.
http://studywiz.herschel.slough.sch.uk/ ... FkM&pid=20
From posts we had last year please be aware that Langley has historically had a cut off score of around 117 and Herschel 112 (even though 111 is a pass) through oversubscription.
It appears that if you put Langley first and Herschel second and achieve a score of 113 then there may be a chance of not getting an offer from either. This is because in the first round of allocations they send out to all 'first choice' applicants and you would remain on the waiting list for Langley without really any hope of getting in.