Yeaterday NPR's Tell Me More had an interview with several parents of children with special needs. Most of the conversation was about finding the right placement for the child, one of the core issues in creating a good IEP. Here is a transcript of the conversation.
I agree with basically everything the parents said. It is really hard to be sure that the district's chosen placement is right for your child. I suggest visiting the placement to see what it is like. If your child is high-functioning, but the other children are severely developmentally delayed, the placement probably is not right. If your child has a cochlear implant and needs auditory stimulation, a classroom focused on sign language education probably is not the right placement. The other thing to do is to track your child's progress. Even if there is not as much progress as a typically developing child, you should see evidence of improvement on a biweekly or monthly basis.
If you are not satisfied with the placement, you should ask for another IEP meeting. There is no rule that IEP meetings can happen only once a year. The fact that you liked the IEP two months ago (or even yesterday) does not mean that you like it today. And lack of progress is a completely reasonable justification to having another meeting with school officials to talk about what can or should be changed.
If school officials cannot explain the reasons for problems, then you should ask what they will do going forward to figure out the problem. Maybe another evaluation is needed. Or an outside expert needs to be consulted. School districts are not required to do what is best, but they are required provide educational benefit. It is practically the definition of a bad placement that it does not provide educational benefit.