Mistake 1: Iterations of Inappropriate Length

The appropriate time length of iterations depends largely on the size of the team involved. A small team of 3 to 4 people might have iterations two to three weeks long. An appropriate length for a medium-size team of 5 to 20 people would be anywhere from three weeks up to six or seven weeks. Teams much larger than 20 may have iterations several months long. These are only rough guidelines. In general, shorter iterations are better. But the larger the project and the more contractors and the amount of ceremony involved, the iteration lengths need to be longer.

I have seen projects with relatively small teams define iterations several months long. This is a mistake. The advantages of iterative development cannot be realized in these situations; these projects tend to resemble and experience the disadvantages of Waterfall projects.

The key is to define iterations that are long enough to get something meaningful completed given the group's size, but short enough to maintain a sense of urgency. Another reason for keeping iterations short is the importance of exercising all the activities involved in the project. In other words, integration, testing, demonstrations, incorporating feedback, and replanning, among others, should be performed frequently. This allows risks to be identified and addressed and needed course corrections identified and implemented quickly. Also, iterations should be of equal length. This allows teams to fall into a natural rhythm.