Exactly. The difference is whether the assessment is seen as feedback or an evaluation/judgement by the students (and the teacher). In the case of marking 100%

Exactly. The difference is whether the assessment is seen as feedback or an evaluation/judgement by the students (and the teacher). In the case of marking 100% on homework -- that's bound to be seen as an evaluation and hence an extrinsic motivator -- not good. Assessing for the sake of gaining feedback on where the students are (for the teacher) and providing feedback to the students on where they are (for the students) is the way to promote intrinsic motivation.