James Lewis is among eight replacements named to travel to Scotland. Also among those named on the bench are Sale Sharks hooker Mark Jones, who comes in for Ben Flower, and Pontypridd prop Nick Eaves, who replaces Kieron Jenkins after returning from suspension.
"The centre is one of our most competitive areas and Gareth brings some extra regional experience to the table having found form and fitness after suffering a broken leg in October," said Rees. "We haven't pushed any panic buttons but we will learn from the mistakes we made last weekend.
"We knew this season would be a big step up for these players after playing U19 rugby last year. This level is the pinnacle of age grade rugby but it can make these boys better players and a better team if we work hard. It will be tough but this season will be great preparation for these players ahead of the IRB U21 World Championships next season.
"Scottish teams always provide tough opposition at age grade level and they will be smarting after suffering a heavy defeat against England last weekend. Once again, we know that the team we meet on Friday at Falkirk will be different from the U19 side we played last season. They are an unknown to us but we are not going to occupy ourselves with their play, we have to concentrate on our own game."
The Scots kicked-off their campaign last weekend with a 31-5 defeat at the hands of England U20 at Bath, conceding five tries.
Wales U20: Martyn Thomas (Llanelli/Scarlets); Alec Jenkins (Llanelli/Scarlets), Gareth Maule (Newport/Dragons), Ashley Smith (Newport/Dragons, captain), Thomas James (Cardiff/Blues); Rhys Priestland, (Llanelli/Scarlets), Robert Lewis (Neath/Ospreys); Hugh Gustafson (Llanelli/Scarlets), Ken Owens (Llanelli/Scarlets), Jamie Corsi (Newport/Dragons), Adam Brown (Bedwas/Dragons), Lou Reed (Llanelli/Scarlets), Danny Lydiate (Ebbw Vale/Dragons), James Harris (Bedwas/Dragons), Lewis Evans (Newport/Dragons)
Replacements (from): Mark Jones (Sale Sharks), Nick Eaves (Pontypridd / Blues), James Down (Cardiff/ Blues), Sam Kiley (Swansea/Ospreys), Darren Allinson (Cardiff/Blues), Rhys Jones (Sale Sharks), Richard Thomas (Aberavon/Scarlets), James Lewis (Bedwas/Dragons)