Is that 20 point bump a comparison taking an expensive prep class to zero preparation? Or is it a comparison taking an expensive prep class to doing self-direc

Is that 20 point bump a comparison taking an expensive prep class to zero preparation? Or is it a comparison taking an expensive prep class to doing self-directed preparation with a $5 prep book? My guess is the former, when the latter is what's relevant for arguments about the advantages obtained through wealth.