Limestone Calcined Clay Cements, LC3, allows CO2 emissions savings up to 40%. The resulting binders have competitive mechanical performances after a week. However, the reactivity of LC3 at early ages is slow and should be improved. Here, we use a multitechnique approach to help in the understanding of early age reactivities which were measured by calorimetry, Frattini assay, and mechanical strengths. The disorder in the kaolinites was quantified by powder diffraction. Some footprints of the local disorder in the resulting metakaolin have been investigated by synchrotron pair distribution function (sPDF). It is concluded that Al-O interatomic correlation position and intensity in the sPDF of the calcined kaolinitic clays could be an additional good descriptor to follow early age reactivity. The results were complemented by 27Al MAS-NMR studies. The rate of the pozzolanic reaction at early ages is governed by the particle size, surface area, and local disorder of metakaolin.