The triumphant Cumbrians completed a second successive unbeaten campaign by overcoming Millfield 8-6 in the wind and rain on Wednesday.
It leaves Sedbergh unbeaten in 36 games in all competitions since they were toppled by Lancashire rivals Kirkham in November 2016.
Since then they have put together two unbeaten campaigns in the Trophy, the national merit table competition sponsored by SOCS, the schools management system, and a tour of New Zealand.
'I'm very proud of the whole squad,' commented head coach Simon Mulholland. 'They work very hard especially our pack who include six boys who are in the lower sixth. They will be back next year.'
A first-half try from wing George Barber gave Sedbergh the edge over Millfield who pressed hard for an upset away win in the second half.
Barber's try was backed up by Tom Curtis, the goal-kicking fly half, who added a first-half penalty to put Sedbergh 8-3 up at the break.
His brilliant kicking has been a feature of the success this season, including a touchline conversion to finish off a terrific comeback to beat Wellington, the former triple Trophy champions, last week, 17-15.
Curtis is now following in the footsteps at the Sale academy of Cam Redpath who guided last year's Sedbergh team.
Barber is at the Newcastle academy alongside Sedbergh captain and fly half Will Haydon-Wood.
The consistency of Sedbergh has been the outstanding feature this autumn while rivals in the 100-strong competition have fallen away.
Stamford provided the biggest surprise by toppling second-placed Rugby School two weeks' ago, 32-21, to ruin hopes of a first title for Rugby.
Third-placed Dulwich lost out in another tight match when London rivals Whitgift won 33-30.
Whitgift, who put together an unbeaten run seven games to put themselves in the top 10, also accounted for Millfield, who are in fourth place, 34-30.
Millfield had looked set to be Sedbergh's biggest rivals but they had an unbeaten run of four games come unstuck when losing to Blundell's, from Tiverton in Devon.
Stamford have maintained the form which toppled Rugby. Their latest win was 55-14 against Loughborough GS. Centre Patrick Harrington and lock Rory Ward both contributed two tries.
Newcastle RGS, who gave Sedbergh a fright before losing in early October, have also maintained their form to the end. They trailed QEGS Wakefield 10-7 at half-time but came back to win 55-10 featuring 31 points in the last eight minutes.
Fly half James Blackett kicked nine out of nine for a tally of 20 points. Centre Chidera Obonna scored two tries and wing Harry Gallagher finished off the last following a 'Barbarian' style move.
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