Two different obverse dies were used by the Ottawa Branch of the Royal Mint
(later to become the Royal Canadian Mint) to produce the Royal Visit school children's medal. Due to production scheduling issues, the Mint was forced to seek outside help with the creation of the dies in order to be able to produce the over 2.5 million medals needed in time for the visit.
The first dies used were prepared by Thomas Shingles while working at a private firm in Winnipeg before he joined the Mint staff. The Shingles obverse has the bust extend to the medal's edge, and is not as artistically strong as the obverse prepared by Percy Metcalfe of the Royal Mint
The Metcalfe obverse -- with space between the medal's edge and bust -- was put into production upon its arrival at the Mint.
I don't know of the mintage split between the two dies.
Hope this helps!