The evidence from the classroom is that the motivation students have for learning a language is the biggest single factor affecting their success. It can take many different shapes and sizes, and experience also shows that a whole range of factors can intervene and interfere with our initial motivation such that it will not necessarily be sustained over time.
Many theories of motivation, such as that proposed by Williams and Burden, are based on the concept of goal achievement. We are initially motivated by our goal to do something, or to achieve an outcome, and the strength of our motivation will depend on the value we give to the goal. A sense of achievement and early successes on the way to the long-term goal are important, otherwise initial motivation can quickly evaporate.
However, the learner's definition of success is not always synonymous with effective language learning. For example, students studying for exams may just want to get good grades, and won't necessarily see the development of good communicative skills as relevant or important. The learners' motivation may work against the development of good communicative skills.
Extrinsic motivators, like passing an exam or gaining a promotion at work, can have a big impact on the strength of motivation at first. Learning methodologies like ESA (engage, study and activate), on the other hand, are based on the premise that learners need to be more emotionally engaged for language learning to be effective. They suggest that intrinsic motivators are more powerful for achieving language learning results, irrespective of where initial motivation comes from. Learners, for example, who have been nominated to study a language by their employer may lack any real affective motivation for study and learning. Their motivation and skills development is more likely to be similar to the example of students studying for exams.
Goal-driven motivation seems to work well with adults, who often have a clear understanding of why they are studying and what they want to get out of it, but what about other age groups? Adolescents' goals are often less well-defined, particularly where they are studying a language as part of the school curriculum. Their motivation can also be complicated by their need for peer approval and to feel good about themselves. Likewise, failure or criticism in previous language learning at school can make adults anxious and erode their confidence, whatever their initial motivations. The issue for young children is much more likely to be boredom rather than learning goals. They generally display enthusiasm for learning and a curiosity about the world around them, but factors like teacher attention and approval, and keeping them entertained, are much more likely to affect their success.
While there is strong evidence for the importance of initial motivation in adult learning, sustaining it, and the factors affecting long-term success, are more complex. Here the teacher and the teaching method play a very large role. Teachers can have a powerful influence on how, or even if, learners remain motivated (after Rogers).
Communicative methods strive to develop language skills by engaging learners in production tasks and topics that allow them to build up the language vocabulary and structures naturally through listening and speaking and thinking out the answers for themselves. They are more likely to be engaged when learning activities are personalised and real for them, and confidence and success is built by ensuring that tasks and topics are matched to learners' language capability. Research into how people learn also suggests that teachers need to vary the activities offered to engage all learning styles, and to ensure that they favour, at different times, learners with different learning preferences.
How the teacher approaches teaching, and her attitude towards her learners also has a big impact on their motivation and success. The teacher's approval, encouragement and recognition is important to building learners' confidence and self-esteem, particularly young children and adolescents. This in turn can be expected to influence their motivation for learning and their success.
The psychology of motivation is complex. It suggests that the nature and level of motivation is key to success in language learning, but experience also shows that exogenous factors can cause motivation to evaporate and undermine success.