I've seen that in the adult textbooks but to be honest, I spend so much time creating my own children's materials, I don't really have time to check out others.
It seems like it might be a good idea. It would get children to think about what they've learned and make a decision about how well they've learned it.
I agree with you that checking the 'poor' box isn't such a grand idea. I also don't think children can really grade their accomplishments so finely, and maybe they don't have to. What I mean is they might not be able to discern the difference between 'poor, with some difficulty, good, fairly good, great.'
I think I'd just have two options:
and younger children would just circle the face. In materials for older children I'd have a check box instead of the faces.
I think that just getting the kids to think about whether they accomplished that unit's goals is enough. In doing so they will self-assess and if they 'lie' on the assessment, that doesn't really diminish the effectiveness of the activity. The students know they are lying.
With those two choices they don't have to choose a 'poor' option and hopefully it wouldn't crush self-esteem and maybe function more as motivation to try to assess yourself as 'great.'
But, I'm not a child psychologist ...