I hate this. Some people at our school did it last year, and they were, without exception, the insanely competitive parents, and it wasn't even dressed up as anything but overt bragging.
I love DS1's school, but the one downside is the open competitiveness among a large cohort of parents. One mother in our class even had to be collared by the teacher and told, in front of everyone, to please put her child's school report away and stop reading it out to all the other parents outside the classroom!
I'd be more than happy to read about a specific achievement by a child who has been struggling, or has just worked really hard to improve. But the people who I've seen posting report details all have fairly bright children, and they are all fighting to prove who is 'top of the class.'
I might make something up and post it, just to send everyone into a tailspin. 'So excited about DS1's Y1 report. So glad the teacher agreed to send him to work with the year 6s for maths. It's really paid off. And such a shame there aren't more than three volumes of Lord of the Rings. He just whizzed through it. Maybe I should give him The Silmarillion next.'