Blimey that's hardcore, and quite an experience seeing glowing cheeks in your classroom! At the schools I went to lads often got slippered in front of the class one or two whacks, proper six of the best discipline with a plimsoll or cane was done in private. The girls were also slippered and caned, but always in private as far as I'm aware.
Sorry, she had to pull them down to just under the cheeks of her bottom. Most were allowed to pull their knickers up after receiving the slippering but a few were sent back to their seat with their knickers still around the tops of their thighs.
The slipper was the staple punishment in my school, although OTK spankings and canings were also delivered. There was one teacher that whenever slippering a girl, he would have the girl bend over and pull her own knickers over her bottom, before lifting her skirt. This excellent video reminded me of those bitter-sweet days!