Re: Seiza by ranks?
We always have some experienced students at the beginners' classes. Last night we ended up with a first kyu, a fourth kyu, and two first-week newbies. By accident of arrival order that was the way we sat down, so we were sorted by rank.
I actually felt quite uncomfortable with this; the newcomers seemed to read it as "us" versus "them" and were noticably uneasy about approaching the seniors to train. Since the reason we have beginners' classes is to train the beginners, not to train the senior students, this is the last thing we want. The senior students made sure to break up the seating order after the first technique and not let it get like that again.
Ordinarily we never line up by rank for anything, even seminars; the only exception is group photos, which put hakama wearers in front. Even the kids, who wear colored belts, don't do it. I wouldn't object to the practice if I were a guest, but I wouldn't commend it to my own dojo.
I visited one dojo that had a tradition of training in gi and white belt, for everybody, in the summer. It was fun trying to guess ranks, especially across a style difference! I usually wasn't off by too much, it turned out.