The company of an imaginary friend used to be interpreted as a sign of a child's deficient character. Writing in a 1934, for example, M. Svendsen said of those children in his sample with an imaginary friend that "personality difficulties were present in most", with "timidity being most common".
Times have changed. It depends on the precise definition of "imaginary friend", but by some modern estimates, nearly half of all young children have an imaginary companion at some point. Moreover, children with imaginary friends have been found to be just as sociable and popular as those without an imaginary friend. Now Gabriel Trionfi and Elaine Reese have presented some preliminary evidence that having an imaginary friend could even be beneficial, tending to go hand in hand with superior narrative skills. In turn, past research has shown that superior narrative skills tend to predict later reading success and school achievement.
Trionfi and Reese interviewed 48 mothers and their five-and-a-half year-old children (half of whom were girls) about whether the children had an imaginary friend now, or had had one in the past. The key finding is that the 23 children with a past or present imaginary friend performed significantly better on average at a narrative skills task. Whether re-telling a short fictional story ("A perfect father's day") to a puppet, or telling a story about a real experience they'd had in the last year, the children with a past or present imaginary friend tended to use more dialogue, and to provide more information about time, place and causal relations, thus providing richer stories.
The researchers aren't sure exactly how imaginary companions and narrative skills are linked, but one possibility is that children with an unseen companion get practice at telling stories whenever they are asked by parents or others about their invisible friend. Of course another possibility, which the design of the current study can't rule out, is that having better narrative skills somehow makes it more likely that a child will develop an imaginary friend.
The researchers say their evidence is too tentative and preliminary for it to be advisable to encourage children to develop an imaginary friend. "Rather, if a child has already created an imaginary companion, parents and teachers could allow this play to flourish."
Trionfi G, & Reese E (2009). A good story: children with imaginary companions create richer narratives. Child development, 80 (4), 1301-13 PMID: 19630910