I have done 3 of the 4 wreck dives to complete my PADI Specialty in Wreck Diving. The first dive was just a orientation to wreck diving, some of the generic do's and don'ts. The second dive was to familiarize myself more with the wreck, remembering key points and doing an external drawing of the wreck on my slate. The third wreck diving I had to again do a drawing with the inclusion of minor peneration and drawing what I saw there. Normally, this is the dive where you get some reel experience, however my instructor was also my cavern specialty instructor, so we jsut reviewed this more to refirm that I could do a knowledge dump of knowledge use.
The fourth wreck to complete will be somewhat of a full penetration with reels, lites, drawings, etc. so my instructor is very intense on knowing all the safety parameters.
One point of advice.... If you plan to penetrate a lot of wrecks, I would highly recommend the cavern specialty as well, simply because wrecks are confined spaces like caverns, and that course teaches you an enormous amount about reels, lites, safety, silt effects and prevention, moving through confined space with little disruption to the evironment.
Hope this in soime way helps....