Because there was what I choose to interpret as "interest" expressed in my previous post, but mainly because I love to talk about myself, I'm going to take a couple minutes to talk through my methods for my shitty school portraits.
It started when I realized that you could fake the "spot light on the backdrop" effect by using a very light backdrop and burning down around the edges. (Yes, the "halo" effect is cheesy, but it is part of the look, and it does serve a graphical purpose.) Also, I did a few "school pictures" for other kids with my 300mm lens, so I could be far away from them. This meant I could get away with a very small backdrop, not much bigger than the child's head. It is literally this thing:
The round things under it are a scrim made from a hula hoop and a sheet, and a barrel thing I have that serves as a seat.
Since I was using a much shorter lens for my kids, not having any 30 foot long straight shots inside my house, I set this shitty backdrop up to Just Barely frame the kid's head. Same barrel, same sawhorse/support for the backdrop. The backdrop is out of focus, some, but basically reads as white with smudges of blue and green watercolor paint. Because that's what it is.
So I also have a somewhat underexposed full frame shot of the same backdrop. Pop that in as a separate layer, adjust color temp/balance to turn the white to greenish/bluish per taste. Then mask and blend the backdrop barely framing the child's face into the other layer of Just Backdrop. Burn the edges down a bit, done and done.
I can't speak for anyone else's kids, but the key with mine is to get them in a good mood, and make the whole shoot last about a minute. So set up in advance, get focus close, then go fetch the kid. Fine tune focus and start shooting/directing, a few seconds later the kid gets to leave. Reward them with candy as necessary. It's basically the same as teaching a dog to sit, a subject about which I also know almost nothing (just ask my dog.)