A direct measurement of the length scale of dynamic heterogeneity in supercooled D-sorbitol has been performed using a multidimensional C-13 solid-state NMR experiment. Several models predict that the growth of this length scale is linked to the slowing of dynamics as the glass transition is approached from above. At 275 K (T-g + 7 K), 2.5 +/- 1.2 nm heterogeneities are detected in sorbitol. This result and recent results of similar measurements on glycerol, o-terphenyl, and poly(vinyl acetate) are compared to various models. The only model in quantitative agreement with these experimental data is based upon local fluctuations in the configurational entropy.