Assessment in the MYP is best described as internal, as opposed to external, because the assessment tasks, strategies and tools are designed, developed and applied by teachers working with students in their schools. The IB believes that teachers are best placed to assess the work of their MYP students; the assessment model supports the professional judgment of the teacher in deciding the levels of achievements of individual students.

The MYP offers a criterion-related model of assessment, so students around the world are measured against pre-specified criteria for each subject group. Teachers modify these criteria to be age-appropriate in the earlier years of the programme.