In the reggio emilia approach, what method is used to assess children's learning

It's more what do you put in front of them to let them try. The example usually discussed has mostly to do with shapes and color and properties than it does with a set curriculum. Light is a usual example of what can be tried. One picture was of a couple of kids (very young) who copied the the pattern of shadows that a picket fence produced. They were engrossed in how to record what it looked like and what angle the shadows made. You have at least 2 subjects that are being appealed to.

The main thing is that the project must be student centered. It is not the teacher's job to design a curriculum; it is the student's. Evaluation is done mostly by camera (taking pictures of what the students do), voice recording and other "visual aides." It is not so much pass fail as it is how done.