The purpose of this study was to examine the effects of a 1-minute stretching programme and 5 weeks of detraining on sit-and-reach score among schoolchildren aged 5-6 years in a physical education setting. Forty-five schoolchildren 5-6 years old from two classes were clustered randomly assigned to an experimental group (n = 23) or a control group (n = 22). During the physical education classes, the students of the experimental group performed a 1-minute stretching programme twice a week for 8 weeks. Subsequently, these participants underwent a 5-week detraining period. The classic sit-and-reach test was performed at the beginning and at the end of the development programme, as well as at the end of the detraining period. The results of the two-way ANOVA showed that the intervention programme increased significantly the students' sit-and-reach scores ("p" < 0.001). However, after 5 weeks of detraining, children's flexibility reverted back to the baseline levels ("p" > 0.05). Although an only 1-minute stretching programme seems to develop the schoolchildren's flexibility, after the 5-week detraining period students' score reverts back to its initial level. This knowledge could help physical education teachers to design programmes that permit students to increase and maintain flexibility levels along the entire academic year.