This study aimed to compare the effect of two types of assessment, i.e., self-assessment and peer assessment, on reflective and impulsive EFL learners’ speaking skill. To this end, a group of 51 (24 impulsive and 27 reflective) intermediate EFL learners were selected based on their performance on a PET (Preliminary English Test), and the Impulsiveness Sub-Scale of Eysenck’s Impulsivity Inventory. They were randomly divided into two experimental groups (i.e., self-assessment and peer assessment), each containing impulsive, and reflective learners. In the self-assessment group, the assessment was based on the Speaking Self-Assessment Sheet designed by Babaii, Taghaddomi and Pashmforoosh (2015). In the peer assessment group, the assessment was based on the Peer Assessment Rating Sheet by Yamashiro and Johnson (1997). At the end of the treatment, the participants received the speaking section of another PET as a posttest. The results of two-way ANOVA revealed that (a) the assessment type and cognitive type had no significant interaction, (b) self-assessment and peer assessment had the same effect on impulsive and reflective learners’ speaking skill, (c) irrespective of the assessment type, learners with different cognitive types performed differently, with the reflective learners outperforming their impulsive counterparts.