I think that educators determine whether a student is ready to move from concrete experiences (real objects/models) to more abstract representations as they find evidence of the student’s concept development improves. According to the Perkins reading, shapes and textures are extremely important. So for example, the way the progression of a cube would be giving the child a toy block. As the student is able to feel and describe the cube and then it is then paired with a 2D version of a textured square. Then just the outline with raised bumps or textured outline would be presented. An interesting step is to make sure that the student is able to draw the shape. This actually reminds me of something I learned, where you know that you understand when you can teach someone else. So I think this is an extremely important step because the student is showing you their understanding of what that square (or object) is by presenting it to you. This now shows you if the student understands the square has 4 corners, equal sides.
Evidence that would be looked for is if the student can identify the real object, recognize the differences amongst other real objects and use language that compares and recognizes features of objects.
If a student struggles with the transition, I would see it as concept gap. For example, in the video the girl was able to recognize the 2D shape as round, with a line on top of it but she wasn’t able to recognize it as an apple because she didn’t know that apples have stems. Since the stem is the concept gap, I would take this opportunity to focus on where apples come from and how they grow from branches (assuming she knows and understands what a tree is). We could focus on how apples grow, parts of the apple. Then have the student reflect why the stem is important. Pairing the functional knowledge, with the real object, may help generalize her knowledge with not only apples but other fruits and vegetables that grow.