In my experience, 5×5 and 7×7 have been very helpful with total beginners, maybe just for 3-5 games each, and of course, them playing black. The fact that on a 5×5 board the Tengen point is on the 3rd line = on the 3-3 point can be emphasised.
BTW, three things I like to show and tell beginners when we begin playing on the 9x9 board (parentheses usually omitted resp. added when I repeat it later):
3-3 lives (if there are no other stones close to it … either in the corner or to one side … if no mistakes or deliberate sacrifice is made … disregarding how big or small.)
A stone on the 3rd line lives (quite probably) if two intersections to both sides are not occupied by the opponent (and no mistakes are made)
two stones on the third line with two free intersections in between live (quite probably … if no mistakes or sacrifices are made)