The County Down school produced a dominant display that yielded six tries, while their opponents replied with a penalty in the last act of the game.
The Dromore pack started superbly and back row Adam Cromwell forced his way over from a powerful drive. Outhalf Alex Walker was unable to convert.
They were made to wait until the 20th minute for their second scorer because of the impressive Fivemiletown defence.
Left wing Adam Walker was the beneficiary after good hands from Kurtis Jackson and Ben Martin. Again, Walkers conversion attempt sailed wide.
Cromwell then completed a first half brace just before the break with a carbon copy of his first effort. Walker's extras brought the half time score to 17-0.
Dromore started the second period as they finished the first, with winger Sam Bothwell crossing for an unconverted score in the right hand corner.
Inside centre Marcus Heath and number 8 Matthew McMaster added the fifth and sixth tries, with Walker converting the latter to give his side a 34-0 lead.
Fivemiletown had missed two penalty attempts earlier in the second half but Stuart Bell stepped up to land three points with the last kick of the game.
The final whistle was greeted with great joy as Dromore celebrated yet another Danske Bank High Schools' Trophy success.