Students don't come with a heap load of self-esteem and belief in their abilities. If they came from mediocre schools they will even have more problems with their belief that meaningful effort will lead to meaningful outcomes. Professors can help those students by being positive and engaging in encouraging dialogue.
Consider a few tips:
-Use active language that creates a sense of urgency.
-Use encouraging words
-Follow up with students and questions.
-When assignments are not turned in consider contacting the student.
-Use specific feedback
-Relate answers to the student.