On average, the black boys I taught behaved far worse than the white ones and had more of a 'chip on their shoulder' attitude. Whilst this is partly due to their family backgrounds being on average less stable and being closer to a 'street culture' of crime and drugs, I believe that it is mainly because no white teacher ever dared to discipline them for fear of being accused of racism, which is the worst thing that can happen to you in teaching. Far better to have robbed a bank or mugged an old lady.
From the day they start school, allowances are made for the black boys and they are punished less harshly and less frequently than the white boys for the same misbehaviour. Kids very quickly work out where their boundaries are and behave accordingly.
Don't forget though, that this is a completely taboo topic in schools. Bringing it up is roughly equivalent to putting a giant Swastika up in your classroom, goose stepping down the corridors and shouting out "Sieg Heil!" when the Head walks into assembly.