Yes I am sure you can apply for WHSB but, if you say you live in Newham have you considered his journey time? Do you plan to move to Essex or work in Essex? It is worth thinking about that as you don't want him too tired to study
C2C West Ham 07.18, arr Chalkwell 08.02, and yes, it is about a 20-minute walk up and over to the Westcliff High Schools. The "down" trains are reasonably quiet at that time, though, so time to get homework done
If you are nearer a station on the Southend Victoria line, Southend High School for Boys is about a 15-minute walk from Prittlewell Station at this end...