Our two (DD yr 8, DS1 yr 12) travel from Chalkwell on the C2C line, but until the middle of July, DD was at Cecil Jones College and travelled by bus through the interchange at Southend Victoria, accompanied by me on Wednesdays as I need to be in Southend then. At about eight in the morning the interchange bus stops are full of mainly SHSG girls (plus CJC and Futures pupils going the same general direction), with SHSB boys and the odd Westcliff / Tommy More pupil waiting for buses going in the opposite direction. Much like the gaggles of Westcliff pupils wending their way up from Chalkwell station at the same time, the general impression is that the activity is a companionable one.
Unfortunately there is no longer a bus going straight down Southchurch Road without going down to the travel centre and back first, but Arriva route 1 stops opposite SHSG. Coming back to the station in the afternoon, I think all the buses which stop outside the school go along Southchurch Rd and stop at Warrior Square - so you can get anything and get off the bus there and (crossing the road carefully at the lights, children
) walk up to Southend Victoria without doing the travel centre loop.
On the train itself there should be lots of company, with boys travelling to SHSB getting off / on at Prittlewell.