When thinking of how best to help a foster child in education, sometimes it's hard to know where to go. Every situation is different, but generally speaking start with the person closest to the issue.
Some top people to contact if your child is having trouble in the classroom or if a foster student in your classroom is having trouble are:
Note how all of these people involved in the life of a foster child do not necessarily intersect and the only person who has experienced all spheres is the foster child himself.
Always begin with the person closest to the problem that needs to be addressed. For example, perhaps you find a foster child consistently is failing his math assessments. Talk with him to see what he has learned up to this point (this obviously will look differently depending on age). Sometimes a foster child is not able to articulate how many schools he's been in or what courses he has already taken. Then, work with him to build a team to help. Ask his permission to talk with his foster parents. Give him ownership as much as possible to solve the problem.
Most academic issues will be solved similarly to how you address issues with other students. The main difference is making appropriate accommodations because of the transitory nature of foster care and being careful to share appropriate information with educational rights holders only. If in doubt of who the educational rights holders are, talk with the foster youth educational liaison.
If an issue is something beyond an academic issue. then you may need to work with foster parents, an educational liaison, or even a social worker. Again, because of the transitory nature of foster care, foster children will experience social and emotional trauma that can affect their behavior in the classroom. If your school has a counselor, ask her advice on how to approach a situation. Don't wait to address an issue because you think a foster child won't be in your classroom for long. That's exactly why you should address an issue.
If you see your child struggling in the classroom, first talk with your child. Ask him how he feels about school (not just the grades he might be getting). Work with your child to come up with a solution and then together (depending on the child's age) discuss a plan to talk with the teacher.
When you talk with a teacher about your child, be careful only to share information that is pertinent to his education. Remember to respect your child's privacy. Oftentimes, knowing a child's history can be important to understanding his classroom performance, but you don't need to outline in detail everything that brought a child to your home.
If you are working with your child's teacher but still feel like he could use extra help, ask to speak with a special education teacher. Many times, even if your child isn't receiving special education services, he may be in a classroom with other children that are and will have a special education teacher already familiar with his classroom performance. If you feel your child needs to be assessed, write a note explaining why you believe this is necessary. See http://lacdcfs.org/edu/forms/index.html for an example form letter (Look under Academic Interventions, Request for SST Meeting).
Contact your child's social worker if you need any help navigating a child's educational rights. Sometimes receiving help is just a matter of knowing you are entitled to it. The Foster Youth Education Toolkit has a section on the educational rights of foster children, which includes information on partial credit allowances and the ability to enroll in a school even if he does not have all of the proper documentation normally required.