I had to read this 3 times to understand what you meant. I should really start drinking less. 
At first, I, for some reason, assumed "class pets" meant high-class pets, as in fancy breeds of cats or owning a white tiger type of thing. Then, I thought "class pets" meant teacher's pet/favourite student but the whole post still didn't make sense. THEN I realised that class pets were just class pets all along. Pets (animals) that are shown/brought to a class of children. 
I need a new brain.