Paul Roos remain top of the Rugby365 rankings after their 44-21 win against Bishops on Saturday.
The Stellenbosch side remain unbeaten and will face another test of their credentials against Paarl Boys High this weekend.
Meanwhile, Transvalia climbed to fifth after beating Helpmekaar 23-20.
The Vanderbijlpark-based school swapped with Gauteng rivals Monument, who suffered an upset 28-26 defeat in a Premier Interschools derby against Waterkloof.
Monnas drop down to seventh, setting up a mouthwatering clash this weekend against sixth-placed Glenwood, who did not play this past weekend.
Other big climbers include Framesby, who beat Boland Landbou 33-20, and Tzaneen-based Ben Voster, who sit at 14th after their 93-12 win against Florida.
Grey College and Paarl Gim round off the top three after victories against Selborne and Rondebosch respectively.
SA Schools top 20 (16 May)
1 Paul Roos
2 Grey College
3 Paarl Gim
4 Paarl Boys’ High
11 Boland Landbou
14 Ben Vorster
Paul Roos 44 Bishops 21
Grey Bloem 62 Selborne 22
Paarl Gim 69 Rondebosch 28
Waterkloof 28 Monument 26
Transvalia 23 Helpmekaar 20
Wynberg 36 Grey Port Elizabeth 33, 36-33
Ben Vorster 93 Florida 12
Framesby 33 Boland Landbou 20
Photo: Thys Lombard