Ok, I discovered that my 8 year old spanish pupils have a problem with left and right.
So, today, I started the class making them raise their left hands than the rights.
Finally I told them to fold their left sleeves (to have a visual reference).
The second step was explaining them how to turn left or right (it's not obvious for them).
Finally we played Simon Says with this (now easy) 4 commands:
Go down 1st (or 2nd...) street