Humans possess a developmentally precocious and evolutionarily ancient Approximate Number System (ANS) whose sensitivity correlates with uniquely human symbolic arithmetic skills. Recent studies suggest that ANS training improves symbolic arithmetic, but such studies may engender performance expectations in their participants that in turn produce the improvement. Here we assessed 6- to 8-year-old children’s expectations about the effects of numerical and non-numerical magnitude training, as well as states of satiety and restfulness, in the context of a study linking children’s ANS practice to their improved symbolic arithmetic. We found that children did not expect gains in symbolic arithmetic after exercising the ANS, though they did expect gains in ANS acuity after training on any magnitude task. Moreover, children expected gains in symbolic arithmetic after a good night’s sleep and their favorite breakfast. Thus, children’s improved symbolic arithmetic after ANS training cannot be explained by their expectations about that training.