In The Social Worker as an Expert Witness in Suspected Child Abuse Cases: A Primer for Beginners, LeRoy Schultz offers guidelines to the social services expert witness:
Before the cross exam, in your pretrial conference with your attorney, you will have discussed the weakest points in your testimony. Ask for directions from your attorney on how to handle these. Be prepared for intense scrutiny of your information, argue well, but not emotionally. The intent of the opposing attorney is to discredit you. Expect denigration and sarcasm but stay calm and professional. You can be discredited in front of the jury by:
1. Lack of licensing or evidence of falsification of credentials.
2. Showing your bias or an unusual interest in court outcome.
3. Presenting evidence of bad character, i.e., misconduct, drinking, owning a pornography collection.
4. Proof of prior inconsistency (in previous trials).
5. Contradictions in your accounts or publications.
6. Lack of knowledge of case or subject matter.
Beware the trap of answering legal questions which only a jury can determine. Offer your opinion but never be drawn out of your expertise, or lured out of your expertise into legal areas, although the opposing attorney may use this tactic. Do not become emotional and defensive on the witness stand – if you have made a mistake in first exam, quickly admit so, and move on.
For more, see http://www.ipt-forensics.com/.