It has been my experience that tape recordings of meetings can be welcomed or not- depending on the school and their school climate towards parent participation. However, I believe that taping is permitted in the United States when the meeting is formal and regards special education placement. As a School Psychologist I have often attended meetings that were taped and it was welcomed.
Also, I just happened to have listened to a radio program today where a special education attorney responded to a question very similar to yours. Her answer was affirmative that tape recording is allowed and in some instances encouraged.
I am a special education teacher and I think that recording a schools assessment for special education placement is very appropriate. During these meetings there is so much that goes on, and sometimes it can be overwhelming. Even though I know our parents get a copy of the report, I think having the recorded version would be helpful also. Good luck!
I do not believe it's legal to record the actual assessment as it is a standardized test. Parents may see the protocols from the assessment. Some parents have insisted on sitting in during the evaluation, but this is not recommended. However, you may record the IEP meeting. Depending on the state, you may have to give a 24 hour advance notice.