That happened to me yesterday with shapes. I knew Ethan had a basic understanding of shapes. He was playing with sidewalk chalk and I decided to draw up some shapes on the ground and see if he could name them for me. Just the exercise of drawing shapes (letters or numbers) and asking if they can identify is great practice. Of course, because it's chalk on the driveway (or sidewalk), it's suddenly a bit more fun. To my surprise, he named them all, except the oval (I was especially surprised when he came up with diamond). By the time we got to oval though, his general answer was "I don't know." He was done--the activity had come to its natural end. So who knows. The moral of that story is that it's a great activity, but don't expect it to be a long one! I think next time we're going to focus more on letters or numbers.
Shortly after, Ethan abandoned the chalk to collect seeds that had fallen on the driveway. Made me chuckle and reminded me an expereince that Becky over at i'm going to make it (after all) had with a similar chalk and shape activity.
Have you had success with a similar activity?