my sensei suggested the 1st lesson we teach should be just rolling back (not full backroll) from sitting and coming back up, very gentle and slow at first, until we determine their level of physicality. Then how to go down to do the same thing from standing, then Tai no henko, and then katatetori shihonage, and especially the ukemi from shihonage, with the ukemi utilizing the skills they were practicing.
I like this progression, and particularly the use of rolling back from sitting both as an assessment tool for the instructor, and a way of getting the students to understand the mechanics of that part of the roll. If you start from standing, as most dojos do, a new student may manage the early part of a backwards fall (getting the foot placed correctly, bending the knee to lower the body), but after that things tend to fall apart -- right at the point where it's most crucial to have the correct mechanics to avoid injury. If you start by teaching the mechanics of what happens after the hip makes contact with the mat, and students have a chance to become comfortable with that, you have a much better chance that they'll be able to do this when they try to fall from standing.