Modern scholars agree that Parten's theory has contributed substantially to our understanding of play, and while alternative classification schemes have been proposed, Parten's stages of play are still widely used. However, there is disagreement on whether there is indeed a sequence of play stages that children go through – for example, whether toddlers are really unable to play cooperatively, and whether solitary play in older children is less common or a sign of immaturity. Alternative explanations suggest that types of play may be influenced by other circumstances (such as how well the children know one another)