Those hardly ever work. I mean, it'd look bad if the teacher couldn't handle their own students so they sent them to the principal's (hell, I don't even know if you're allowed to do that anymore, most of them just send kids to other teacher's rooms, but that doesn't resolve anything) and a lot of kids don't care if they get detention and they don't care if you call their parents and a lot of parents don't care if their kid's acting up in school.
If a kid and their parents don't care about detentions, do you really think a suspension is gonna be any different? I would think a problem kid would view a detention as bad since it takes away from something good (ie I have to stay after school so I cant go home and play, or I can't go out to recess) while a suspension would be seen as something good (ie Woot! I got a 5 day weekend!)
Well, detentions don't really affect the parents. I mean, a detention is just kinda the equivalent of hanging out with some friends after school so it doesn't affect the parents much. However, if there's a suspension and the kid is left home all day, that's more big of a deal (did that make sense?). I mean, at my school, you get detention for chewing gum but suspensions are a lot more serious.
Or all three.