It's absolutely possible to sleep train in attachment parenting and co-sleeping way. But I don't actually like the term "sleep training" because I think it brings up connotations of dogs and having an action and a reaction. That if you do one thing, it will come out one way. I don't believe that relationships with humans work. I think if sleep patterns need to be changed in a household because they are not working for whatever reason, I think parents need to be able to tell their children what the changes are going to be before hand and give the child time to prepare. Then be willing to support a child when the change is occurring. Just because a child knows a change is coming doesn't mean they will necessarily happy with it. It doesn't mean that you don't need to support them through it and get the outcome that you want.