Tangible user interfaces (TUIs) embed computer technology in graspable objects. This study assessed the potential of Topobo, a construction toy with programmable movement, to support social interaction in children with Autistic Spectrum Conditions (ASC). Groups of either typically developing (TD) children or those with ASC had group play sessions with Topobo and with LEGO[TM]. We recorded the extent and sequence of different categories of play during these sessions. For both participant groups, there were more social forms of play with Topobo than with LEGO[TM]. More solitary play occurred for LEGO[TM] and more parallel play occurred with Topobo. Topobo was also associated with more time in onlooker and cooperative play in TD. Finally, we observed differences in play sequences between TD and ASC children, and discuss how different play materials might produce specific patterns of play in these two groups. (Contains 1 note, 2 tables, and 6 figures.)