I went to a comp.
This behaviour isn't 'standard', but I don't think it would be that unusual in certain catchment areas - e.g. those close to 'caravan parks'.
Being clever wasn't cool and I was bullied and unpopular. All classes were disrupted by a minority of idiots. I sat in class, zoned out the chaos, and read the (very interesting) textbooks. The teachers were, as a rule, actually very good and genuinely cared about the kids.
For sixth form I attended a grammar school. Some of the teachers very much looked down on the intake of kids from the comps and the assignment of teachers was, in my opinion, very unfair - we got all the crap teachers. Occasionally, we'd have another teacher cover a lesson and the difference in quality was stark. Unsurprisingly, none of the comp kids did very well at A Levels - which probably reinforced their prejudices and resulted in the crap teachers being assigned for the next comp intake. The fact that none of the comp parents were familiar with the teaching staff, probably helped them get away with it.
Seeing how the kids, who attended the grammar from the age of eleven, have done in later life, I'd say they certainly instill a level of self belief that just doesn't exist in standard state schools.
We have grammar schools in our area and will try to send our boys there. I might even be tempted to 'return home' and send them to the boy's grammar in my home town.