For some years now, we have been working with assignments that require our students to evaluate their answers themselves, i.e. they compare their answer with a sample answer.
We have found that many of the students struggle to do the self-assessment. From this we conclude that they have not learned to do this. They lack skills in metacognition and self-directed learning, in our view.
See also: https://link.springer.com/collections/bfciggbeha
What skills in metacognition and self-directed learning need students to self-assess their asseignments or tasks?