The size of children’s oral vocabularies at age 2 may predict their eventual readiness for kindergarten according to a new joint study from Penn State, Columbia University and UCLA Irvine.

After analyzing the vocabularies of 8,650 2-year-old children around the United States, researchers followed up three years later to evaluate those children’s academic and behavioral skills. “Our findings provide compelling evidence for oral vocabulary’s theorized importance as a multi-faceted contributor to children’s early development,” says lead author Paul Morgan. The full study can be found here in the journal Child Development.