Is this the tool you have? What is going wrong?

The problem I remember when we were learning to use it was that the "screwdriver"
part would push the slotted part out of the bearing before the slotted part got wedged in there good
enough to push the bearing out too. The solution was not being timid. I wish I remembered
the exact details, we did something like: put the slotted part in the bearing, and lay the
wheel down on the floor so that the slotted part is on the floor and can't come out. Then,
in an un-timid fashion, give the screwdriver part a few good whacks so that it is wedged
deeply enough in the slot that the slotted part is also wedged tightly enough in
the bearing. Then lift the wheel up vertical and whack the bearing out by hitting
the end of the screwdriver part. If the slotted part comes out without the bearing coming out,
you didn't seat the screwdriver part deeply enough (assuming there's nothing
weird going on, like someone welded the bearing in there...)...
-Mike