In the US slips to landing are actually REQUIRED to be demonstrated.
And as for those who say you can't teach slips in a C152/172... not true. Slips with the flaps down are fine in a C152 and are not recommended in a 172 with full flaps. So you put in 10 degrees, slip the plane down and then drop the rest of the flaps before the flare. It works great.
Weasil