The metaphor of the mental number line accounts for numerous empirical effects of spatial-numerical associations. In the present study, we aimed at investigating directional spatial-numerical associations reflected by SNARC-like digit-direction and sign-direction congruency effects as well as the sign-digit compatibility effect when 6th graders performed magnitude comparisons of multi-symbol numbers (i.e., positive and negative numbers). As spatial-numerical associations were associated with sensorimotor experiences, we used whole-body and finger tapping responses to manipulate the extent of motor responses. We only observed a SNARC-like digit-direction congruency effect, but neither a sign-direction congruency nor a sign-digit compatibility effect. This indicates that 6th graders may already have developed spatial-numerical associations for absolute number magnitude, but not yet for polarity signs. Furthermore, not observing a sign-digit compatibility effect seemed to suggest that 6th graders may not yet process multi-symbol numbers in the same parallel componential way as adults do. We argue that while 6th graders are able to process negative numbers, they are not yet automatically associated with space or integrated in the place-value structure of the Arabic number system like multi-digit numbers are at this age.