I'm intrigued by your 0 vs. 1 experiment. I wonder if there is something fundamentally different in how we learn the concept of ordinal numbers (1, 2, 3) versus, say, integers (-1, 0, 1). Usually we teach numbers by counting physical objects, and perhaps it takes a little longer to understand the concept of zero if you're used to counting objects.
I'm intrigued by your 0 vs. 1 experiment. I wonder if there is something fundamentally different in how we learn the concept of ordinal numbers (1, 2, 3) versus, say, integers (-1, 0, 1). Usually we teach numbers by counting physical objects, and perhaps it takes a little longer to understand the concept of zero if you're used to counting objects.