If the Church openly said that it preferred middle class kids over working class kids this report wouldn't be surprising at all.
It could also be the other way around or both. Middle class parents could be very keen to get their children into English Roman Catholic schools. My experience is out of date going back to 1982/1983 but for what it is worth middle class parents then wanted the 'discipline' that Catholic schools provided. There would be a surge of attendance at church from the lapsed Catholics just before putting forward their kids' names for entrance.
I, however, was not impressed with the psychological effects that the school's discipline was having on my 4 year old son. I use to collect him during work lunch and deliver him to my my wife's work place. Normally he was very chatty but one day he was completely silent. I asked him why and he confessed that he had done something very evil. So, evil that he begged that I would not tell his mother. Very surprised I asked him what this terrible deed was. He said that he had climbed up on top of a double decker bus. This he was obviously not capable of and finally he broke down and admitted that the teacher had caught him showing an evil interest in his little todger during toilet break. He was taken out of that school pretty sharpish. Sick perverted teacher