Originally posted by Tim Griffiths
Also called suwari kokyu ho, its an exercise that leads to the pin that we've all assumed you're talking about.
It begins with both partners sitting seiza opposite each other, about a fist's width between each other's knees, with one partner holding both wrists of the other. Tori then takes uke's balance in one way or another, and leads that to one side, so that uke falls/half rolls onto their back (and the pin we think you mean.
Many dojos use this as the last (sometimes first) exercise of every class.
(Its usually called kokyu dosa in ki-style dojos, kokyu ho is the usual name in an aikikai dojo).
Ah yes, that is exactly what we were doing. Thank you, now I know what it is called.
And we did do it as the last exercise in class too.