How do you guys deal with your child if he or she starts making friends with the naughty or more troublesome kids in school?

I think keeping him or her from being friends with these kids might only make them more appealing. First, I would explain to my kid that no one is perfect. But, that they should strive to always be well-behaved. I'll point out what qualities of these said friends shouldn't be mimicked. Be firm and set limits. But also listen to your child. Ask them why they are friends with these kids. Perhaps, there are admirable qualities in them that parents fail to see by boxing them into the "naughty" category. Kids need love and attention. Mostly, they need guidance. Sometimes, all it takes for "naughty" kids to change is having good friends around them and elders who believe in them. Teach your kid how to be a positive influence on them instead of the other way around.