Competence-based, science e-testing (CBSeT) is a novel external assessment tool which provides feedback to science teachers about their students' competence-based skills, thereby giving relevant assessment information which teachers could potentially use in their teaching practice. The aim of this study was to determine the extent to which teachers' existing beliefs toward CBSeT enabled them to use the received CBSeT feedback in their practice. Semi-structured interviews were conducted with eleven science teachers from selected schools which took part in an CBSeT pilot program. The findings revealed that most teachers believed the feedback provided adequate assessment information about the level of students' actual competences and gave general guidelines to support their further teaching and students' learning. At the same time, they perceived that the CBSeT feedback was currently lacking an accountability function, which would make students more responsible for their learning and provide feedback on the effectiveness of their own teaching. Despite the teachers' generally positive attitudinal beliefs toward CBSeT, several constraints to operationalizing the feedback in the classroom were identified. Based on these findings, the paper suggests ways to facilitate further implementation of CBSeT feedback in the classroom.