Luke McGrath is promoted from the bench to take the scrum half spot, in the only change to the Irish back-line.
A reworked pack sees James Rael join Peter Reilly and Kyle McCall in the front row. Iain Henderson moves from five to four and will partner Daniel Qualter in the second row.
Conor Gilsenan moves across the back row with Aaron Conneely coming in to join Jack Conan in an athletic combination.
Tadhg Beirne, Jordan Coghlan and Kieron Marmion are named in the replacements along with Callum O'Connell who comes into the 22 for the first time.
Commenting on his selection and of the task at hand, Ruddock said: "We have reinstated a few of the lads that were involved in the win against France. We felt that they deserved to come back into the equation for this test.
"We certainly don't underestimate the Scottish side, I have looked at their tapes and realise that our defence are going to have to work very hard to stop them crossing the line.
"We have prepared to the best of our ability and are ready to front up to a very talented Scotland team."
Friday's game will be broadcast live from Dubarry Park on RTÉ Two.
IRELAND UNDER-20 Team & Replacements (v Scotland Under-20s, RBS Under-20 6 Nations Championship, Dubarry Park, Buccaneers RFC, Friday, March 9, kick-off 7.05pm):
15 - Shane Layden (Buccaneers/Connacht)
14 - Conor Finn (Buccaneers/Connacht)
13 - Chris Farrell (Dungannon/Ulster)
12 - JJ Hanrahan (UL Bohemians/Munster)
11 - Foster Horan (Lansdowne/Leinster)
10 - Paddy Jackson (Dungannon/Ulster) (capt)
9 - Luke McGrath (UCD/Leinster)
2 - James Rael (Garryowen/Munster)
3 - Peter Reilly (Lansdowne/Leinster)
4 - Iain Henderson (Queen's University/Ulster)
5 - Daniel Qualter (Buccaneers/Connacht)
6 - Conor Gilsenan (UCD/Leinster)
7 - Aaron Conneely (Corinthians/Connacht)
8 - Jack Conan (Old Belvedere/Leinster)
16 - Callum O'Connell (Galwegians/Connacht)
17 - Des Merrey (Clontarf/Leinster)
18 - Jake Cawley (Old Belvedere/Leinster)
19 - Tadhg Beirne (Lansdowne/Leinster)
20 - Jordan Coghlan (UCD/Leinster)
21 - Kieron Marmion (Corinthians/Connacht)
22 - Cathal Marsh (Dublin University/Leinster)
23 - Stuart Olding (Belfast Harlequins/Ulster)
Ireland Under-20s' 2012 Fixtures/Results:
Friday, February 3 - Ireland U-20s 11 Wales U-20s 6, Dubarry Park, Buccaneers RFC
Saturday, February 11 - France U-20s 12 Ireland U-20s 13, Stade des Alpes, Grenoble
Friday, February 24 - Ireland U-20s 27 Italy U-20s 8, Dubarry Park, Buccaneers RFC
Friday, March 9 - Ireland U-20s v Scotland U-20s, Dubarry Park, Buccaneers RFC, 7.05pm
Friday, March 16 - England U-20s v Ireland U-20s, Adams Park, London Wasps RFC, 8.05pm