What science or psychology is behind the Landmark Forum's coursework?
This isn't a direct answer to your question .

I got the sense that Landmark was in the same category as other so called 'power' therapies such as neurolinguistuc programming etc. The 7:30 report - a credible Australian current affairs program - did an story on Landmark last year. 

References

http://www.abc.net.au/7.30/content/2011/s3367386.htm

Devilly, Grant J. (2005) "Power Therapies and possible threats to the science of psychology and psychiatry", Australian and New Zealand Journal of Psychiatry, Vol. 39, No. 6, June 2005, pp. 437-445(9)