Strange as it may seem, when the flight is for instruction, neither the student nor the instructor needs to be current for landings under 61.57(a) and (b). It doesn't matter who is acting as PIC (for legality of flight it never matters who can log PIC).

Here are the two FAA Legal opinions that deal with it:

Kortokrax
http://www.faa.gov/about/office_org/...kraxinterp.doc

Olshock (student pilots)
http://www.faa.gov/about/office_org/...kraxinterp.doc