It came against much-fancied France, with the tournament leaders finally edging a tight 18-13 win at Netherdale.
With that in mind, Lineen has made just four changes for their trip to Wales with Ben Chambers rested while Jack Cosgrove misses out through injury.
The prop is replaced in the front row by James Malcolm who moves from hooker with Sam James taking over the No.2 jersey.
Gavin Lowe and Ben Vellacott come off the bench to start at stand-off and scum-half respectively with Cameron Fenton, Sean Yacoubian, George Horne and Angus Rennie coming onto the bench.
And with the Welsh, who have won just two games in the Championship, coming into the game off the back of a 67-7 loss to England, Lineen is looking for his side to push on again from last week.
"The belief is coming for our guys. We still lost the match but parts of our game are up to scratch. We're looking to have gained a lot of confidence after last weekend," said Lineen.
"We know how difficult this game is going to be and I expect the guys to front up. We need to play the game in the right area, get the set piece right and have to keep striving to improve.
"The guys are looking to get involved in the Junior World Championship squad and they'll be fighting hard to make an impact."
SCOTLAND UNDER-20 TEAM TO FACE WALES UNDER-20
15. Damien Hoyland (Melrose)
14. Jamie Farndale (Edinburgh Rugby)
13. Blair Hutchison (Loughborough Univiversity)
12. Ruairidh Young (Edinburgh Accies)
11. Sam Pecqueur (Edinburgh Accies)
10. Gavin Lowe (Glasgow Warriors)
9. Ben Vellacott (Hartpury)
1. James Malcolm (Ayr)
2. Sam James (London Wasps)
3. D'arcy Rae (Ayr)
4. Andrew Cramond (Aberdeen Grammar)
5. Lewis Carmichael (Melrose)
6. Tommy Spinks (London Scottish)
7. Gabriel Carroll (Loughborough University)
8. Magnus Bradbury (Edinburgh Rugby)
16. Isaac Miller (Loughborough University)
17. Cameron Fenton (Howe of Fife)
18. Phil Cringle (Edinburgh Rugby)
19. Glen Young (Newcastle Falcons)
20. Neil Irvine-Hess (Edinburgh Rugby)
21. Sean Yacoubian (Glasgow Hawks)
22. George Horne (Currie)
23. Angus Rennie (Aberdeen Grammar)