Fig. 4

One-factor model (left) and level of spatial-thinking model (right) for ratings of teaching difficulty. One-factor model (one); negligible (neg), optional (opt), and required spatial thinking (req). The math problem were labeled first by type: visual (V), word (W), and notation (N); second by context: real-world (R), abstract (A), and notation (N); and third by level of spatial thinking: required (Q), optional (P), and negligible (G). Since notation types were also notation contexts, we balanced the number of problems by including two of each of these problems (indicated with a 1 and 2)