Every teacher knows the feeling: an unplanned occurrence in the classroom has all your pupils hooked but, with time running out, you have no choice but to steer them back towards the lesson plan.
But now a new book, inspired by a radical approach to education in Italy, shows what can happen when the script is tossed to one side. It features the story of a Stirling nursery where shadows cast by an upturned overhead projector sparked a year-long project straddling a wide range of subjects.
Stirling nurseries have for 15 years been using a pioneering approach to education inspired by the Italian city of Reggio Emilia, where schools are founded on the belief that children can take control of their own learning from infancy.
The impact of the approach across the globe is explored in Reggio Emilia Encounters, a new book edited by early years consultant Pat Wharton and Linda Kinney, former assistant chief executive of Stirling Council.
One chapter details what happened when children at Croftamie Nursery became fascinated by their own shadows and were sent off to learn more about the subject.
The pupils' studies led to them creating a book about a giant who was so big that he blocked out the sun, which was given to local libraries and put up for sale. This in turn piqued the interest of children in other classes, who set about establishing the height of the giant from clues mysteriously left for them to find.
The work of the original group of pupils "spread like a contagion throughout the nursery to the point that everybody was buzzing with the happenings that emerged from the project", according to the book's chapter on Croftamie, written by headteacher Lorna Willows and her predecessor Annie Miller.
All the nursery staff became involved, taking the project in a number of unexpected directions, covering topics such as scale, the seasons, hibernation and animation.
"The learning that emerged from working with this project, for all staff - experienced and new - felt at times seismic, and almost impossible to comprehend," the authors write.
Key to success was a willingness to take risks, along with the underpinning philosophy that the nursery's pupils were "capable, rich and resourceful".
The lessons of the project could be applied well beyond the preschool sector, according to Ms Wharton, who believes that a "scripted, preordained approach" is restrictive at any age. "There's no reason why these values can't go right through the education system," she said.
Ms Wharton added that pupils' work must be constantly documented - whether it be in wall displays, video clips, on laptops or in some other way - to remind them of what they have achieved, and to inspire parents to get involved and develop projects in yet more unexpected directions.
"People sometimes think this is anarchy," she said, "but it's not. The children are so engaged and interested and researching all the time, and being listened to and valued. There isn't anarchy - we've never had that experience."
Staff expertise was still required to nudge children in directions that they may not have thought of themselves, she said, although "letting go, not being in control, can feel a bit scary".
Although she acknowledged that cuts to Scottish education budgets and falling teacher-pupil ratios could hamper nurseries' and schools' willingness to experiment with the Reggio Emilia philosophy, Ms Wharton said the benefits for those teachers willing to take a risk were myriad.
"If you listen to the children and follow their interest, that's the fundamental thing - it's the values that are most important," she added.