http://www.youtube.com/watch?v=HL7ItVWO-B
This video, from the wonderful Géraldine, explaining the traditions of April Fool’s Day, in France:

When I was teaching, April Fool’s Day would sometimes fall in the Easter holidays – very disappointing because we didn’t cover how this date was celebrated in France. However, when we were in school, my pupils had enormous fun designing their ‘poissons d’avril’.

Later, when working as a consultant, I had the pleasure of visiting a primary school on 1st April. The headteacher, of this school, was a real character and told the pupils that if anyone managed to stick a ‘poisson d’avril’on her back, without her knowing, they would win an Easter egg! Unfortunately, I had to go to my next school before I found out the result but I admired the headteacher ‘s enthusiasm.