Traditionally, both judges and lawyers looked on witness "coaching" with considerable suspicion. Judges were concerned about lawyers subverting the judicial process by using their witnesses as a "mouthpiece" for the lawyer to improve their cases. Lawyers were suspicious of other lawyers for the same reason. No one considered the plight of the witness very much.
Fear of speaking in public is the single phobia endorsed by more than 2/3 of all respondents in surveys of the US public--no other fear comes close to these numbers. Testifying in court is not only "speaking in public", it is also accompanied by the very common fear that testifying falsely will lead to a jail sentence (I know of no research detailing the prevalence of this myth, but my guesstimate is that nearly 2 out of 3 witnesses believe it.) Lawyers who live their professional lives in the courtroom frequently don't appreciate how intimidating the setting and the jargon can be to someone experiencing it for the first time. And, when the witness believes that their children are on the line, the fear and pressure rise exponentially.
The research cited below nicely highlights the primary value of witness training: IMPROVED accuracy of the testimony! What Ellison and Wheatcroft found was that training witnesses about the rules and tactics of cross examination led to a REDUCTION in errors in responding accurately by more than 66% to complex questions on cross examination. Accuracy of answers to simple cross examination questions improved by 52%. Just as importantly, witnesses reported having the confidence to ask the cross examiner to clarify questions.
More than 25 years of teaching people how to testify effectively has convinced me that witness training, done right, not only helps the witness but significantly aids the administration of justice. This research confirms that belief. Of the hundreds of people whom I have trained, NOT ONE has ever said the training about how to testify effectively, especially how to handle cross examination, was a waste of time. Not one.
Now that the advantages of witness training to the system as a whole have been documented, there is no reason not spend the time to provide witnesses with the tools they need to testify accurately. Justice would seem to require it.
Ellison, L. & Wheatcroft, J. (2010). "Could you ask me that in a different way please?" Exploring the impact of courtroom questioning and witness familiarization on adult witness accuracy. Criminal Law Review, 11, pp. 823-839.