Niet zo, maar zo

Sent by Heleen (the Netherlands).

Illustration by Fiep Westendorp (1916-2004): "Tien geboden voor ouders" (='Ten commandments for parents'), published in Het Parool (20 October 1960). I admire the works of this illustrator, and I am happy to have received some drawings of her so far.

I received this postcard some months ago, but I decided to post it now that here the school year is starting. In fact, this is a school for parents. The teacher is showing to the parents how to act: "Niet zo, maar zo" (='Not this/that way, but this/that way').  

It arrived inside an envelope. For this reason the post-worker couldn't see what was written in the blackboard. So (s)he didn't know the right way to cancel the stamps...