England last faced the Baby Boks 12 months ago when they fell to a 36-29 defeat at the University of Western Cape, and Fletcher says that he is expecting another physical content.
"We know that they are strong side," he said. "They tend to be big up front and have some quick backs. But saying that, we have a big pack and we're looking forward to the game massively.
"It's been pretty wet since we got here but the lads have trained well. It's a good experience for them, and it's a new experience for most of them. But this is the first of our three games and we're looking to start well."
Captain James Chisholm added: "We're really pleased to be here and excited about playing our hosts. South Africa in South Africa is about as tough as it gets, but we're ready and we can't wait to get out there."
England Under 18 starting XV against South Africa
15 Howard Packman (Moulton College & Northampton Saints)
14 Tom Howe (Shiplake College & London Wasps)
13 Nick Carpenter (Filton College & Bristol Rugby)
12 Max Clark (Bryanston & Bath Rugby)
11 Nathan Earle (Oaklands & Saracens)
10 Sam Olver (Oundle School & Northampton Saints)
9 Stuart Townsend (Ivybridge Community College & Exeter Chiefs)
1 Alex Lundberg (Hampton School & London Wasps)
2 Cameron Neild (Manchester Grammar & Sale Sharks)
3 Paul Hill (Prince Henry's Grammar & Leeds Carnegie)
4 Tom Ellis (Millfield & Bath Rugby)
5 Charlie Ewels (Bryanston & Bath Rugby)
8 James Chisholm (Brighton College & Harlequins) (C)
7 Lewis Ludlow (Hartpury College & Gloucester Rugby)
16 Jack Walker (Prince Henry's & Leeds Carnegie)
17 Luke Chapman (Truro College & Exeter Chiefs)
18 Ciaran Parker (St Ambrose & Sale Sharks)
19 Josh Peters (Oundle School & Northampton Saints)
20 Ellis Genge (Hartpury College & Bristol Rugby)
21 James Mitchell (Lymm School & Sale Sharks)
22 Will Owen (QE Leicester & Leicester Tigers)
23 Josh Sharp (Oaklands College & Saracens)
24 Rory Jennings (Bryanston School & Bath Rugby)
25 Josh Skelcey (Moulton College & Northampton Saints)
26 Tom Fowlie (St Pauls Catholic College & London Irish)