Thanks,
I found now it is indeed the Wall painting of the Atoom building designed by Hein Stolle
(architect and furniture designer)
the 737 seems to be a coincidence.
It is the top row of what appears to be an Arabic digit puzzle.
displayed in the painting.
During the Atoom exhibition there was a square with a pond in front of the building.
A visit to the AreoPlanorama would fit perfectly in the school trip.
As the AeroPlanorama opened in 1960, this would narrow it down to spring or early summer 1960 before the re-painting of the aircraft.