Learmonth, who is a pupil at Longridge Towers School, was in superb form beating German U18 champion Marcus Halbache and the Danish champion Muno.
Not for the first time this season, due to weather conditions, Learmonth had to resort to getting involved in a tactical race.
He went through the first lap shadowing the German Halbacke, but with 250m to go he made his move and gradually pulled away and won by a clear 10m in a time of 1min 57sec.
Learmonth now goes on to the English Schools' Finals in Sheffield in two weeks time. The event is live on Sky Sports for all finals on the Saturday.
Learmonth will also be running on the pro-circuit this weekend where he will take on one of the Borders greatest ever 800m runners, Colin Welsh of Kelso.
It should be a fascinating clash as both runners will probably be off scratch. Both are running close to the Scottish native record of 1min 53sec and that record could well be under threat this weekend.
Meanwhile, Andrew Crichton from Innerwick continued his good form winning the Jog Scotland 5km road race at Dryburgh Abbey in a fast time of 16 minutes on a very undulating course.