Collett played 50 minutes at hooker, while Tonks was on the field for 65 minutes at full back as England came from behind to record a narrow victory.
A penalty try, along with an earlier effort from Tom Casson of Sale Sharks and a penalty and two conversions from Newcastle's Rob Miller sealed the win for the tourists who had trailed 8-3 and then 16-10 with just 10 minutes remaining.
England U-18s coach Chris Kibble said: "Despite a fairly disjointed game, both sides tried to play open, attacking rugby and England were rewarded for their strength of character and determination, particularly in the last 10 minutes, to pull off the victory.
"It is particularly encouraging that the side picked for this match included nine players who will return to England U-18s next year."
England U-18s team:
1 Ben Moon (Ivybridge Community College/SWERA), 2 Tom Collett (Wyggeston & QE College/Leicester Tigers), 3 James Currie (Millfield/Bath Rugby), 4 Peter Elders (RGS High Wycombe/London Wasps), 5 Dan Williams (Ivybridge Community College/Gloucester), 6 Alex Gray (Barnard Castle/Newcastle Falcons), 7 Jacob Rowan (Bradford Grammar/Leeds Carnegie), 8 Carl Fearns (Sedbergh/Sale Sharks, captain), 9 Daniel White (Hymers College/Leeds Carnegie), 10 Robert Miller (Keswick/Newcastle Falcons), 11 Charlie Sharples (St Peter's High/Gloucester Rugby), 12 Tom Casson (Sedbergh/Sale Sharks), 13 Ben Williams (Bryanston/Bath Rugby), 14 Henry Trinder (Hartpury College/Gloucester Rugby), 15 Greg Tonks (Nottingham High/Leicester Tigers).
Replacements: 16 Joe Marler (Sussex Downs/Harlequins), 17 James Clark (London Irish), 18 Greg Bateman (Cranleigh/Harlequins), 19 Calum Clark (Barnard Castle/Leeds Carnegie), 20 Joe Trayfoot (Epsom College/Harlequins), 21 Tom Sargeant (RGS Guilford/Harlequins), 22 Oliver Frost (Bromsgrove/Worcester Warriors), 23 Rory Clegg (Barnard Castle/Newcastle Falcons), 24 Mike Stanley (Oaklands College/Saracens), 25 Oliver Winterbottom (Rednock/Gloucester Rugby), 26 Jack Wallace (Aylesbury Grammar/London Wasps).
Substitutions: Marler for Moon (45), Joe Clark for Collet (50), Calum Clark for Elder (17), Trayfoot for Fearns (blood, 67), Frost for White (43), Clegg for Miller (69), Wallace for Tonks (65).