Wales then went through as top qualifiers from the group to play Australia in the Cup quarter-final before bowing out of the main competition with a narrow defeat to the Aussies.
However the young side bounced back to record a 12-5 victory over Argentina in the semi-final of the Plate before being taught a valuable lesson in the Plate final against Samoa who ran away with a 31-12 win.
"Everybody played a big part in last week's tournament but the trick is now to finish off the season with a big performance in London," said John.
"Scotland's event was the first time we made a Plate final since the third event in Port Elizabeth which was pleasing.
"Against Samoa we were very competitive in the first half but only had something like two possessions whereas every time they had possession they scored a try. And that proved crucial so that was a big lesson for us."
Looking back on last weekend's displays, John paid tribute to his side which had two new recruits in teenagers Sion Bennett and Thomas Grabham.
"The first game against Scotland was a tough one to start with as the home side were under pressure to perform in front of their home crowd. I was pleased the way the boys handled themselves to come away with a narrow 17-14 win.
"The boys continued that with a good effort against Russia where we scored some good tries to come away with a 31-5 win.
"Going into the game against South Africa we felt we had a chance. We ran them close in the Hong Kong Sevens and with them three or four players down due to injury we knew that if we were clinical we would run them close.
"South Africa were still a very strong side but the boys limited their errors, our defence was good, the receiving from kick-offs was good and we scored some good tries in what was a very mature position from the boys. So to top the group unbeaten with a 17-5 win over South Africa was very pleasing."
This weekend in Twickenham, Wales have drawn Fiji, Spain and Zimbabwe. Fiji will start as firm favourites to qualify top of the pool but Spain and Zimbabwe will both be difficult obstacles to overcome believes the Wales head coach.
"Our group is a tricky one for lots of reasons," explained John. "Spain are a very difficult side to play against. They've pushed New Zealand hard and did well in Scotland last weekend. They won the FIRA competition last year so they won't be any pushover by any stretch of the imagination while Zimbabwe have the capacity to cause a few headaches as well so to suggest Fiji are the only ones to worry about is wide of the mark."
Wales: Thomas Grabham, Rhys Jones, Lee Williams, Alex Walker, Dan Fish, Rhys Patchell, Ifan Evans, Rhys Shellard, Adam Thomas, Sion Bennett, Richard Smith, Craig Price