I've just got back from a few hours in school and managed to grab a quick chat with a highly qualified, expereinced and wise member of staff who holds an SPLD diploma.
She has watched the footage several times over, and while we all agree that he was a very naughty little boy, her take on the incident was interesting. She suggested it could be a case of over disciplining and too much disapproval directed at the boy. Apparently if you watch all the video, at some time before Charlotte was laying into her brother about sucking his thumb, (actually copying and making fun of him), Mike was giving the evil glare, William leaned across with a frown to his wife, and Kate was doing her best to correct Louis in a reasoned manner. It could be likened to a pile on, and the little lad felt he was being told off from all angles. Often there is sadly no escape from this but to live up to the bad name others are giving, especially when you are cornered and can't articulate your feelings in a difficult situation
Moreover she notice that the little boy started slapping himself, so he obviously acknowledged his own misdemeanours afterwards.
As I said before, I think people should cut Louis and his mother some slack, or try to understand the predicament.