Stonham, a lock or No 8, is part of a squad who are made up of seven players who started out in the school's prep section.
'We've got a team who have gelled together and really enjoy their rugby,' director of rugby Andrew Le Chevalier, the former Wasps prop, said.
'It's good to field a home-grown team in a national competition.'
A strong Saracens connection is made up of Stonham, scrum-half Sam Bryan and prop Harry Sturge who scored two tries in a 21-0 win over Bedford School on Tuesday.
Oakham provided the sternest test so far but two late penalty goals from Bryan settled the contest, 28-22.
The three wins put Felsted in third place in this competition sponsored by the school management system, SOCS.
The Essex team are unbeaten after wins over Haileybury, Oakham and Bedford
And champions Sedbergh, who are unbeaten in five games, will have to be at their best throughout the autumn to fend off a number of challengers.
Dulwich, who host Eton on Saturday, completed three wins in a row thanks to a late try from flanker Olu Odunlamni, who raced from his own 22 to help pip Brighton College, 22-17.
A quick start by Brighton had earned them a 12-0 lead before Dulwich responded to lead 17-12 at half-time, MikelDavies, Jack Springate and Max Bliss scoring tries.
Whitgift showed they have learned from defeats by Sedbergh and Wellington to beat Warwick,23-19, and John Fisher,41-5, in four days this week.
Wing Charlie Cadogan scored two tries against local rivals John Fisher following one against Warwick.
Clifton, who travel to Marlborough on Saturday in the annual Governor's Cup, one of the oldest fixtures in the rugby calendar, are unbeaten in three after wins over Monmouth, Sir Thomas Rich's and St Edward's.
Champions Sedbergh will have to be at their best throughout the autumn