By joining the same high school class study group, the indication is that there will be no introduction of new study ideas, and if we as former high school classmates happen to rank poorly in relation to our colleagues, we could at best retain the lowly performance, and remain on the left tail of the plotted histogram- the poorly performing lot. Even if we ranked well in relation to classmates, it would still be necessary to distribute ourselves among the groups, to attract diversity of views and fresh study styles. Therefore I would favor a group not dominated by my former high school classmates.