John rings changes for another tough test against South Africa

The Scots will face a South Africa side that dispatched fourth-seeded Pool C opponents Tonga 40-14 in their previous match.

That result will have given the South Africans renewed confidence that they can lift this year's trophy after they finished third last season.

John said: "We've committed the Australia game to our memory bank of experience. Playing at that level of intensity for the whole match puts a yardstick on the players' experience and on their expectations of themselves.

"Playing two back-to-back southern hemisphere teams in five days is an intense environment that you have got to learn from. We've played in it, we've analysed it and now we have to learn from it."

Under-20 debuts have been offered to hooker Anthony Kent and prop Adam Fedorciow in a new-look front-row which sees prop Colin Philips – who started every game in this season's Six Nations – return to the front-line.

The third under-20 debutant, Michael Fedo, will start at open-side flanker, moving David Denton to lock in place of Robert Harley, who starts on the bench.

Injuries to inside-centre Alex Dunbar (rib), stand-off Duncan Weir (chest), and lock Robert McAlpine (neck) mean James Johnstone, Matthew Scott and Grant Gilchrist come in as direct replacements. Gilchrist will be making his long-awaited return to the second-row following a leg injury sustained in the 2010 Six Nations opener against France in February.

Moseley's Callum MacBurnie will win his first start at under-20 level and will partner Johnstone in the centre, pushing Michael Tait to the wing and Oliver Grove to full-back in place of Tom Brown, who starts on the bench.

The final change sees blind-side flanker Callum Stidston-Nott replace Michael Maltman, who is also relegated to the bench.

Scotland Under-20 team

(to play Australia at the Estadio CA Colon, Santa Fe, today 8pm BST)

Oliver Grove (Worcester Warriors);

Michael Tait (Newcastle Falcons), Callum MacBurnie (Moseley), James Johnstone (Currie), Dougie Fife (Currie);

Matthew Scott (Currie), Alex Black (Leeds Carnegie);

Anthony Kent (London Scottish), Adam Fedorciow (University of Bath), Colin Philips (Stewart's Melville), David Denton (Edinburgh Accies), Grant Gilchrist (Stirling County), Callum Stidston-Nott (London Scottish), Michael Fedo (Watsonians), Stuart McInally (Watsonians, captain).

Substitutes: Alun Walker (Currie), George Hunter (Glasgow Hawks), Robert Harley (West of Scotland), Michael Maltman (Heriot's), Russell Weir (Loughborough Students), Tom Brown (Edinburgh Accies), Jonny Kennedy (Sale Sharks).