Harry Thacker, Harry Rudkin, Javiah Pohe and George Catchpole all started the 25-13 final victory over Ireland in Madrid.
England Under-18s lifted the Justin Bridou trophy after tries from hooker Thacker, centre Pohe and Newcastle Falcons prop Scott Wilson. Fly-half Billy Burns contributed seven points, and replacement Sam Olver added a penalty.
The win rounds off a faultless season for the England squad following wins over France, Scotland, Georgia and Wales.
England got off to a dream start with a try after just two minutes as a swift move across field opened up space for Thacker to dive over.
The second try came on the quarter-hour mark as patient build-up eventually freed Pohe who showed a nice step before going over the line for his third try in as many games in Madrid.
Head coach John Fletcher said: "We've gone unbeaten all season which in my eyes is a Grand Slam. We're really pleased with all the efforts throughout the campaign.
"A lot of these guys were in the Under-17 squad last season and they've come through and worked extremely hard and they deserve this win against Ireland. They deserve everything they get. Their effort, commitment and work rate was excellent and considering the nature of the game it was a really good performance."
England Under-18
15 Zach Kibirige (Yarm School) (Newcastle Falcons)
14 George Catchpole (Leicester Grammar) (Leicester Tigers)
13 Tom Stephenson (Moulton College) (Northampton Saints)
12 Javiah Pohe (Wyggeston & Queen Elizabeth 1st) (Leicester Tigers)
11 Joshua Watkins (Bromsgrove School) (Worcester Warriors)
10 Billy Burns (Hartpury College) (Gloucester Rugby)
9 Callum Braley (Hartpury College) (Bristol Rugby)
1 Harry Rudkin (Wyggeston & Queen Elizabeth 1st) (Leicester Tigers)
2 Harry Thacker (Leicester Grammar) (Leicester Tigers)
3 Scott Wilson (Sedbergh School) (Newcastle Falcons)
4 Maro Itoje (Harrow School) (Saracens)
5 Charlie Ewels (Bryanston School) (Bath Rugby)
6 Ross Moriarty (Hartpury College) (Gloucester Rugby)
7 Gus Jones (c) (Eton College) (London Wasps)
8 Joel Conlon (Ivybridge Community College) (Exeter Chiefs)
Replacements
16 Reece Marshall (Moulton College) (Northampton Saints)
17 Danny Hobbs-Awoyemi (Moulton College) (Northampton Saints) on for Harry Rudkin 38 mins
18 Alex Lundberg (Hampton) (London Wasps)
19 Jake Oldaker (Wellington College) (Bath Rugby) on for Charlie Ewels 57 mins
20 Josh Buggea (Hartpury College) (Worcester Warriors) on for Joel Conlon 47 mins
21 Tom Chapman (Colfe School) (Saracens) on for Callum Braley 55 mins
22 Sam Olver (Oundle Schhol) (Northampton Saints) on for Billy Burns 55 mins
23 Nick Carpenter (Filton College) (Bristol Rugby) on for Javiah Pohe 63 mins
24 Nathan Earle (Oaklands) (Saracens)
25 Max Northcote-Green (Millfield) (Bath Rugby)
26 Howard Packman (Moulton College) (Northampton Saints)
