A consulting expert works under counsel's direction and does not testify. A testifying expert prepares a disclosed report and gives deposition and trial testimony. How far work-product protection extends in each role, and what becomes discoverable once an expert is designated, are legal questions that vary by forum. The practical side, how the engagement is organized so that either path stays open, is what this note covers.
When to start as consulting
When counsel doesn't yet know what the numbers show. When the damages theory is untested. When the first task is to evaluate the opposing expert rather than to build an affirmative case. In each of those situations, a consulting engagement lets the analysis proceed while the designation decision waits.
Keep the streams separate
If a consulting expert is later designated to testify, work from the consulting phase may become a subject of discovery. The practical protections are simple: a separate engagement letter or amendment for the testifying role, separate files, and separate billing codes from the day the role changes. Mixing the two makes every later argument about scope harder.
Log what counsel provides
Keep a running log of the facts, data, and assumptions counsel provides and the date each arrived, and keep every version of the model. Testifying experts are typically asked to identify the facts and assumptions they relied on, and a log built in real time is far more reliable than one reconstructed at deposition.
Keep clean compensation records
Rate, hours, and invoices. A testifying expert's compensation is typically disclosed, and it will be asked about. Compensation is never contingent on the outcome of a matter.
Maintain the testimony list
A running list of prior testimony (case caption, forum, year, and whether by deposition or at trial) is something counsel will need at designation. Maintaining it continuously is easier than reconstructing it under a deadline, and it is provided to retaining counsel on request.