My company is trying to prove the point to a customer that traditional
classroom training alone may not be the most effective way to
introduce a new corporate practice.

Here's my question:

Can you point me to relevant, referenceable statistics regarding
knowledge loss after taking a traditional classroom course? (Example:
After one week, students forget 60% of what they learned.)

Thanks you for your help!

I can tell you that Adults learn by hearing, seeing and doing.
Training material is typically designed so the main point of what you
are trying to teach or train is repeated at least once in one fashion
or another. (i.e. summary statements or questions withing a chapter)
It is true that after an amount of time students will forget some of
what they have learned. That is why repetition is important. You may
want to try contacting the American Society for Training and
Development (ASTD) to see if they have some study that will support
and give hard numbers to the question you are asking.

Peddlegirl - Thanks for the hint. I will give it a try right now as
our Account Manager is eager for an answer. Thanks a million. I
appreciate it.