A structured curriculum for classes is something that is often missing in martial arts schools. The most common approach is the “technique of the day”, where an instructor would show a few random techniques during class, often without any unifying theme or continuation of previously taught material.
If they’re more diligent, instructors might prepare a week or two worth of material in advance, hopefully covering the same theme or related positions.
The problem with those kind of approaches is that it makes it harder to acclimate new members and beginners into the art. This is especially true for Brazilian Jiu-Jitsu and other ground fighting arts, due to the amount of different positions one might encounter while sparring, and because most of the movements feel very unnatural for beginners.
(This post is based on my experience training in BJJ for close to a decade, and thus uses BJJ instruction as reference. It should be applicable to every martial art though).