A theory is an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena. All practice is informed by both informal theories that individuals construct from their social experience and formal theories that have a more deliberate and academic beginning. These formal theories of practice are official, formally recorded and evidence based. Their basis is in formal teaching and research. Because they are explicit they are open to question. Practice theories are founded in practice wisdom, informal knowledge and assumptions. They are based on observing events, and are culturally transmitted. Whilst they are and adaptable to practice, because they are implicit, they can be difficult to question. Good practice draws knowingly on both and is aware of the limitations of each.
I think "good" ideas emerge in a cycle. Experience (our own and other people's) is important, but we can learn poor practice through experience as well. Experience requires reflection - what has gone? well what hasn't? what could I change? etc - but whatever is learnt in one specific case is not always generalizable to others. So I think we also need theory and research. This is sometimes hard for residential workers, after all they have often come to the work to do a practical job and want to work with children, but we need to be able to look at our practice in the light of what theory explains and what research confirms. Reading, studying, training are all part of this, but need to be integrated into practice. And I think there is one other vital ingredient: what the lives and voices of the children/young people say. They are experts in their own experience, and "good" practice needs to be experienced by them as good, both in the here and now and in terms of outcomes.