Research has shown that the beneficial effects of peer collaboration are not always apparent until some time has elapsed. Such delayed effects are not readily incorporated in current models of collaborative learning, but because they constitute incubation effects in the psychological sense of the term, they should in principle be consistent with cognitive accounts of how incubation occurs. Accordingly, the paper reports three studies which test whether, in accordance with cognitive models of incubation, the delayed effects of peer collaboration could result from: (a) the breaking over time of unhelpful mental sets, (b) the engagement in post-collaborative reflective appraisal, and (c) the experience of subsequent events that, thanks to collaboration, can be used productively. The studies involved 9- to 12-year-old children working on the factors relevant to floating and sinking. The results provide no evidence for the relevance of set breaking or reflective appraisal, but suggest strongly that peer collaboration can 'prime' children to make good use of subsequent input. It is argued that in addition to clarifying how the delayed effects occur and applying incubation models in a novel context, the results flag up issues that are common to collaborative and cognitive theory, and that neither address adequately.

Occasions where children oppose each other have been claimed to convey intellectual benefits through their association with justification and resolution. They have been claimed to promote social rejection through their association with aggression. Because it is inconceivable that intellectual benefits imply social costs, either the relation amongst opposition, justification, resolution, and aggression is weaker than claimed, or children differ in their use of justification, resolution, and aggression during opposition. To explore these possibilities, 49 triads, comprising children aged 4 to 7 years, were videotaped while they engaged in free play and structured activities. The children varied in gender and temperament, and the triads varied in gender composition. Justification, resolution, and aggression were all relatively frequent in oppositional contexts. However, the use of justification and resolution during opposition was clearly separated from the use of aggression. Gender, temperament, age, and gender composition of triad were all relevant to the oppositional behaviour that children displayed.It is paradoxical that the treatment in the developmental literature of occasions where children oppose each other is itself contradictory. On the one hand, there is a tradition that treats opposition as providing a major impetus to intellectual growth. The tradition can be traced to Piaget's (1932) work on moral development, which proposed first that progress depends on coordinating current beliefs with alternatives in contexts of mutuality and equal status, and second that opposition during peer interaction has the potential to provide both alternative beliefs and the requisite contexts. Subsequent research has supported Piaget's views, showing how oppositional encounters between children can promote understanding of conservation and spatial transformation

Occasions where children oppose each other have been claimed to convey intellectual benefits through their association with justification and resolution. They have been claimed to promote social rejection through their association with aggression. Because it is inconceivable that intellectual benefits imply social costs, either the relation amongst opposition, justification, resolution, and aggression is weaker than claimed, or children differ in their use of justification, resolution, and aggression during opposition. To explore these possibilities, 49 triads, comprising children aged 4 to 7 years, were videotaped while they engaged in free play and structured activities. The children varied in gender and temperament, and the triads varied in gender composition. Justification, resolution, and aggression were all relatively frequent in oppositional contexts. However, the use of justification and resolution during opposition was clearly separated from the use of aggression. Gender, temperament, age, and gender composition of triad were all relevant to the oppositional behaviour that children displayed.

It has long been acknowledged that justificatory speech is linked with both social and cognitive development. Yet many studies suggest that pre-school children might lack the ability or experience to produce such discourse in routine interaction. In contrast, researchers such as Eisenberg and Garvey (1981) have found evidence of pre-schoolers' justifications in conflictual play contexts. Although this has positive implications for child development, the conflictual context may sit uneasily with parents' and teachers' expectations. It is encouraging therefore that McWilliam (1999) has demonstrated that pre-schoolers can produce justificatory dialogue in both conflictual and nonconflictual situations, even if occurrence in the latter context is less frequent. Based on this, the aim of the present study was to encourage pre-schoolers' production of justificatory discourse during peer exchanges in a non-conflictual context. Twenty-two dyads from a state-run nursery were subject to verbal modelling of either justificatory speech (experimental condition) or a more commonly used alternative (control condition) in daily ten-minute sessions over five consecutive days. All interactions were videorecorded for subsequent coding and analysis. Results showed that both 'why' questions and 'justifications' were significantly higher in the experimental condition, indicating that pre-schoolers' explanatory speech can be effectively enhanced by a cooperative intervention programme.

We conclude that women in the high WHR group may find adherence to diets problematic because the desired change in shape does not occur.