Mean joint engagement state percentages for the pre- and post-intervention groups and, for comparison, for typically-developing toddlers at 18 months of age from an earlier study (Adamson et al., 2004). NSI cord = non-symbol-infused coordinated joint engagement, SI cord = symbol-infused coordinated joint engagement, SI sup = symbol-infused supported joint engagement, and NSI sup = non-symbol-infused supported joint engagement. Other includes time spent in object engagement, unengaged, and person engagement. Right-upward strips represent supported and right-downward stripes represent coordinated joint engagement; gray shaded stripes in the middle represent their overlap with symbol-infused joint engagement.