Harmen is chairman of the Jazz Piano Faculty at the Conservatorium van Amsterdam / University of the Arts Amsterdam. He teaches the principal subject of Piano Jazz, ensembles, coaches student groups, and Master electives.

Harmen is frequently invited to give workshops and masterclasses throughout Europe. He was a guest at the conservatories of Brussels (BE), Antwerp (BE), Gent (BE), Oslo (NO), Leuven (NO), Rotterdam (NL), The Hague (NL), Utrecht (NL), Tilburg (NL), Maastricht (NL), Zwolle (NL), Manhattan School of Music NY (US) – for an online masterclass, Bergen (NO) and also was several times part of the faculty of the International Jazz Summer Workshop in Siena (IT).