Oliver Parkison kicked a penalty and Alex Schwarz converted Andrew Oakden's try to keep the U16s interested, but tries from wing Ryan Evans and hooker Alun Rees, plus 10 points from the boot of outside half Tom Carpenter earned the Ospreys a crucial away win.
The Under 18s put up their best showing of the season so far against a strong Ospreys side. Playing the first half in to the teeth of a strong wind, the North remained on level terms until a missed tackle in midfield allowed Ospreys full-back Tom Brydie to score in the corner.
Deeke Morse squeezed past three defenders to score a second. A third followed just before half time, through Matthew Morgan who added his second and his side's fourth shortly after the interval.
A spell of intense North pressure culminated in a try for Joe Sproston mid way through the second half and a comeback looked a real possibility when Callum Goulding raced in for an interception try. However, a try from Ospreys captain Lloyd Peers made sure the visitors came away with the victory.