You can use the scaling method but you need to scale it to 0 from one keyframe to the next. So add a keyframe at the last frame you want the object to be full sizes. Then go to file/animation setup, the top set of options is the current time, in the frame# option box type in the next frame ..ie: if it's at frame 35 type in 36, this moves the time line to frame 36, then scale the object to 0 and add another keyframe. Now the object should go from full sized to nothing between frame 35 and 36. The frames per second shouldn't matter because your going by frames, but is real imported to set a keyframe at the last frame you want the object to be full sized or else it will start scaling down before it gets to that frame.

Stephen Ray