Having beaten Russia 46-11 in their opening game, and then fallen by a point to South Africa, 27-26, the Welsh side have secured seven points to date with their thrid and final Pool game to come.
The young Springboks, who are the defending champions, and the All Blacks have each picked up a maximum 10 points to date and meet in the crunch game in round three. Two other unbeaten sides, Australia and Ireland, both have nine points each.
The Irish face France, who are tied on seven points with Wales, while theWallabies face Argentina. The winning team picks up four points and there is a bonus point on offer for four tries.
That means the winning side can pick up five points, while the losers can earn two bonus points if they score four or more tries and finish within seven points.
The first thing the Welsh have to do is win if they are to progress into the final four and to do that they will have to avenge their 22-19 defeat in the Six Nations championship earlier in the year at Kingsholm.
Wales beat England in this competiton in South Africa last season and lead 7-3 in the 10 match series betwen the two countries at this age level.
Victory at Raeburn Place, Edinburgh on Saturday (kick-off 4.00pm) would be another feather in the cap of Welsh coach Chris Davey.
Davey has made two changes from the team that fell to the young Boks. Scrum half Richie Rees and centre Lee Thomas, who between them supplied 16 points against South Africa, give way to James Ireland (Cross Keys) and Steven Ireland (Cardiff).
Wales Under 21: Ricky Williams; Mattew Nuthall, Andrew Bishop, Steven Ireland, Chris Czekaj; Nick Macleod, James Ireland; John Yapp, Kieran Crawford, Cai Griffiths, Alun Wyn Evans, Tom Brown, Jonathan Edwards (capt), Gavin Quinnell.
Replacements: Ian George, Will Kay, Jonathan Mills, Richard Dale, Richard Rees, Matthew Jones, Lee Thomas.