Why do Newell and Simon consider production systems good theories? There's an early article by Newell, detailing some of the flaws (as he sees them) in experimental psychology, and what production systems have to offer, in You can't play 20 questions with nature and win, in Visual Information Processing, edited by Chase (PSY BC:C 39).
For a more recent approach, sometime during the course you should certainly look at Unified Theories of Human Cognition by Newell, also in our library. Try to read the first four chapters.
Finally, please read Richard Young's chapter on Production Systems for Modelling Human Cognition in Expert systems in the micro-electronic age edited by Michie (E.U.P. 1980) (in the Psychology library and RSL). Pay particular attention to the three levels of modelling he distinguishes, on page 43.