From Slavin (2009): "Extrinsic incentive: A reward that is external to the activity, such as recognition or a good grade" (p. 313).

Extrinsic incentives should be used when clear expectations are expressed, clear, immediate and frequent feedback is provided, and the value and availability of extrinsic motivators is increased (p. 316-319).

Praise can also be an extrinsic incentive. "Contingent praise: Praise that is effective because it refers to specific task performances" (p. 320).