Despite the benefits of peer assessment, many teachers are not willing to implement it, particularly for low-achieving students. This study used the theory of planned behaviour to predict pre-service teachers' intention to use peer assessment for low-achieving students. A total of 229 pre-service teachers in Singapore participated in the survey which consists of eight factors about peer assessment in writing: belief of knowledge source, belief of ability, belief of constructivist assessment, attitude, subjective norm, perceived behaviour control, behavioural intention, and intention for low-achieving students. Structural equation modelling was used to test hypothesized relationships of the eight factors. This study found that pre-service teachers' beliefs about knowledge source and constructivist assessment significantly influenced their attitude towards peer assessment of writing. In addition, the attitude and perceived behaviour control were significant factors in shaping the intention of peer assessment. Lastly, pre-service teachers' intention of implementing peer assessment for low-achieving students was influenced by both the intention of peer assessment and the belief of ability.