This is an excerpt written by Lucas Blair from the book The Gamification of Learning and Instruction.
Let’s contrast Measurement and Completion achievements, which describe two distinct conditions under which we reward players for their actions. Measurement achievements are given to players for completing a task to a certain degree. Their performance can be measured against another player’s performance, their own performance, or some standard set by game designers. An example of this would be the star rating used in Angry Birds, which gives the player a number of stars based upon how well they beat the level.
A measurement achievement can be likened to feedback because it is evaluative in nature. The literature regarding the use of feedback in training and education indicates that feedback is beneficial to players because it allows them to reflect on their performance in relation to goals they have set for themselves . This reflection increases the player’s perception of competence, which in turn increases their intrinsic motivation; a term used to describe a task one finds inherently rewarding . That increase in perceived competence could also mediate the negative effects of other design decisions, like overusing rewards, which decrease intrinsic motivation.
On the other hand, completion achievements do not tell the player how well they’ve performed the task; instead they are offered as an award once a task is completed. Completion achievements can be split into two subcategories: performance contingent achievements and non-performance contingent achievements. Performance contingent achievements require skill to complete while non-performance contingent achievements are awarded for simply being present.
Performance contingent completion achievements, like those received for finishing a dungeon for the first time in World of Warcraft, can be better understood by reviewing what we know about the use of rewards as an extrinsic motivator. Some incentive programs have been shown to have a significant positive effect on task performance. However these types of rewards can decrease a player’s sense of autonomy, especially when given in excess . This decreased sense of autonomy leads to lower intrinsic motivation. Rewards also create an artificial ceiling for performance at the reward threshold . Once players have earned the reward they are unlikely to continue on with the task that they were persuaded to do. For game developers this translates into the replay value of their game.
Using rewards makes players less likely to take risks, as they do not want to hurt their chances of being rewarded . This is especially relevant to rewards used in video games where designers wish to encourage creative and experimental play.
Non-performance contingent achievements, like earning an article of clothing or a pet for attending an in-game event, have no negative effect on intrinsic motivation. However these types of rewards do not have a performance measure, so players are unlikely to be interested in earning them unless they are paired with some sort of social reinforcement.
Use measurement achievements instead of completion achievements to increase intrinsic motivation through feedback.
 Locke, E. A., & Latham, G. P. (2002). Building a practically useful theory of goal setting and task motivation: A 35-year odyssey. American Psychologist, 57(9), 705-717.
 Deci, E. L. (1975). Intrinsic motivation. New York, NY US: Plenum Press
 Deci, E. L., & Ryan, R. M. (1985b). Intrinsic motivation and self-determination in human behavior. New York: Plenum.
 Csikszentmihalyi, M. (1975). Play and intrinsic rewards. Journal of Humanistic Psychology, 15(3), 41-63.
 Amabile, T. M., Hennessey, B. A., & Grossman, B. S. (1986). Social influences on creativity: The effects of contracted-for reward. Journal of Personality and Social Psychology, 50(1), 14-23.
Here are some resources focused on gamification and games for learning:
Click here to visit a catalog of Resources on this subject.