His personal interest at that time was the interaction between the personality of children and the teaching environmental instruction (Aptitude Treatment Interaction 'avant la lettre'). In 1965 he continued his professional career at the University of Utrecht, and became a full professor in 1972, after taking his doctors degree (on Field Independency in a teaching/learning situation). In 1983 Dick Snow (Stanford), Eric de Corte (Leuven), some others and he initiated EARLI: the European Association for Research on Learning and Instruction. In the same year Franz Mönks invited him to meet with Joseph Renzulli. This started things to move. He managed to get financial support from the Dutch government for scientific research on identification and instruction of gifted students of secondary schools in the Netherlands.
1987 Joan Freeman, Harold Wagner and he founded ECHA. As we know now: very successfully. They even tried to carry out the message on the need of gifted education in African and Asian countries. In his lectures and workshops he emphasized the subject 'learning to learn' by gifted students. After his retirement from the university, he and two other colleagues started a private consultancy on giftedness in 1991 (PABU). They have worked with parents, schools and universities to accommodate gifted children. They implemented Renzulli's idea of Compacting Enrichment into a working model for Dutch schools. At 2013 his part in the PABU is limited. It is a great pleasure for him that the University of Utrecht is willing to incorporate the PABU in the near future. His efforts will be continued.