I used a 22" softbox on a 300W strobe, with a diffuser installed inside the box, and a grid to focus the light to a small area. The strobe was mounted on a C-stand, with the softbox pointing nearly straight down (tilted slightly forward). You can see the setup in the raw shot here:
Lining everybody up to be illuminated evenly took a couple minutes, and only about a dozen shots were taken before we had one that was perfect. Some simple edits and cropping got to the final result rather easily, and I must say, I think I very faithfully recreated the look of the original photo!


