Let's talk flashbacks

Doing flashbacks

I realized for my fic that I need to tell the back story of someone's teenage years to have it make sense why they're doing what they're doing, so I'm writing some flashback scenes. My question is how to insert them.

I don't know if I want to do them as chapters themselves, or maybe disperse them throughout inside other chapters. I can make either work, but I'm not sure which would be most effective.

How do you do yours (if you do them)?