Having already qualified from the pool, the visitors completed the double over the Gwent regions thanks to Dale Ford.
The outstanding centre, who has been an ever present in the side this season, kicked two penalties before the interval and converted his own try in the second half.
The Dragons put up some stern resistance and a converted try after the break kept them within touching distance of a Scarlets side led superbly well by No.8 and captain Steffan Phillips.
On Friday, the Scarlets Under 16s entertain Blues South at Kidwelly (2.30) needing to defeat their visitors with a bonus point and without conceding a losing bonus point.
Scarlets U16: L Treharne; G Hunter, L Harbatt, R James, P Rushesha; J Williams, R Williams; G Thomas, S O’Leary, S Lee, D Evans, J Gardiner, R Bloomfield (capt), O Powell, C Morris. Replacements: N Bowen, A Williams, D George, D Coleman, J Iles, R Evans. M Jenkins.
