In front of the Argentina vice-president, England ran in 17 tries as their visit officially opened new facilities at the Mendoza club, with London Irish wing Marcus Watson scoring a hat-trick.
Jacob Rowan, Sam Edgerley and Christian Wade scored two each and fly-half George Ford kicked 11 conversions.
England now face one further warm-up game, against Uruguay on Wednesday, before taking on Argentina in an international test match on August 3.
England coach John Fletcher said: Im delighted with the teams performance. We went into the game wanting to put the opposition under pressure when they had the ball and also when we did. We did that and our attack was very good, with all players showing a high level of understanding and skill.
Forsyths third try of the tour came during the first half as England reached the interval 52-3 in front.
England Under-18s
1 Joe Marler (Harlequins), 2 Jamie George (Saracens & Haileybury), 3 James Currie (Bath Rugby & Millfield), 4 Tom Holmes (Sale Sharks & Sandbach), 5 James Gaskell (Sale Sharks & Sandbach), 6 Sam Jones (London Wasps & Aylesbury Grammar School), 7 Jacob Rowan (Leeds Carnegie & Bradford Grammar), 8 Alex Gray (Newcastle Falcons & Barnard Castle, captain), 9 Jordi Pasqualin (Gloucester Rugby & The Kings School), 10 George Ford (Leeds Carnegie & Rishworth), 11 Sam Edgerley (London Irish & Wellington College), 12 Owen Farrell (Saracens & St Georges), 13 Andy Forsyth (Leicester Tigers & QEGS Wakefield), 14 Marcus Watson (London Irish & St Georges College), 15 Tom Catterick (Newcastle Falcons & Barnard Castle).
Replacements: 16 David Blackwell (Gloucester Rugby & Hartpury), 17 Mako Vunipola (Bristol Rugby & Millfield), 18 Jamie Gibson (London Irish & Marlborough College), 19 Joe Barker (Leeds Carnegie & QEGSWakefield), 20 Sam Harrison (Leicester Tigers & John Cleveland College), 21 Rory Clegg (Newcastle Falcons & Barnard Castle), 22 Christian Wade (London Wasps & RGS High Wycombe), 23 Joe Cobden (Leicester Tigers & King Edward VI Lichfield), 24 Jack Wallace (London Wasps & RGS High Wycombe).
Substitutions: Blackwell for George, Vunipola for Currie, Barker for Gray, Wade for Watson (all HT), Wallace for Forsyth, Clegg for Farrell, Harrison for Pasqualin (all 43 mins), Cobden for Catterick (52 mins)
Tries: Vunipola, Watson (3), Currie, Catterick, George, Rowan (2), Forsyth, Edgerley (2), Holmes, Wade (2), Wallace, Harrison. Conversions: Ford 11