A research project is described in which students aged 11-18 years were offered computer-produced sentences about four everyday changes in materials. They were asked to indicate whether the sentences made sense to them. In their styles of commentary upon their own responses to the computer sentences, students gave incidental evidence of the degree to which they were willing to speculate beyond the knowledge about which they felt individually secure. The authors argue that confidence and willingness to speculate are of value to students learning science and should be fostered
