We have created a little coding dojo to demonstrate you the difference between a clean and a dirty implementation of the same task.
The procedure (exemplary):
The participants are divided into two groups, a clean and a dirty one. Initially, everyone works on his own way. At the beginning of the dojo every participant gets a zipped file via eMail at the same time. The zip consists of a Maven project containing a main class (implementing a little parser) and one belonging test class. The goal is to accomplish a marginal requirements change.
When the task has been done what can be verified by running the test class (all test “are green”) the developer sends a message back to the organizer. After this session the response times can be calculated and compared together per group.
Optional resources for the clean version: