If someone has an explanation for her academic performance, we can describe this explanation in three ways. They may be internal or external; may be stable -- or constant -- or unstable; or they may be controllable or uncontrollable. There is a pattern to the way in which people explain their own performance, which is that people tend to explain it in a way that allows them to maintain a positive self-image.
The four main explanations for academic performance involve ability, task difficulty, effort and luck. Some of these are internal, such as ability and effort. Some of them are stable, such as task difficulty. Only effort is controllable.
How people perceive themselves -- how they explain their performance -- can determine their actual performance. For example, if someone believes he has low ability and is unlucky, and that these are the main determinants of how well he does, he's likely to have low motivation. The belief that leads to the best motivation is that both success and failure are caused by effort. Effort is something the learner can control: He can achieve if and only if he applies himself.
It's necessary to encourage a student to believe she's competent, and that she's capable of good achievement if she applies the necessary effort. Any tasks set, therefore, must be achievable. The correct idea of effort is learning time dedicated to doing effective tasks. Evaluating students can be made partly on the basis of effort. For example, with coursework, it's always necessary to apply a reasonable level of effort to produce something of a good standard.