Teachers need to be aware of the situation the kid is coming from. They need to know if this child is really behind academically, or if the student is having difficulty concentrating. Also, foster kids really lack continuity. They don't take for granted that you'll be there for them. Many kids are really severely traumatized and then put in a school situation where they're expected to pay attention.
Trauma changes children's development and the speed with which they develop.
They shouldn't be expected to fix social problems. But they have to know the kid is legitimately having a hard time, that it's not just a case of a bad child who can't adjust. Educators should become aware of the problems and find the appropriate person to help. I'm often able to give educators information about a student's family background. But, too often, teachers wait until they notice something going wrong with the student before they ask for information.