We present a measurement of the correlation between the spins of t and View the MathML source quarks produced in proton–antiproton collisions at the Tevatron Collider at a center-of-mass energy of 1.96 TeV. We apply a matrix element technique to dilepton and single-lepton+jets final states in data accumulated with the D0 detector that correspond to an integrated luminosity of 9.7 fb−1. The measured value of the correlation coefficient in the off-diagonal basis, View the MathML source, is in agreement with the standard model prediction, and represents evidence for a top–antitop quark spin correlation difference from zero at a level of 4.2 standard deviations.