This study investigated the possibility of enhancing the level of preschoolers number sense by introducing two intervention programmes, "Lets think!" and "Young children with special educational needs count, too!" Forty-five preschoolers, mean age 66.4 months, were randomly assigned to the experimental and control groups. The experimental group received instruction twice a week, for half an hour, and for a period of nine months. Pretest?postest comparison revealed that the experimental group showed enhanced number-sense performance immediately after the instruction ended, but the between-group difference faded after six months. There were no statistically significant differences between the groups in general mathematical thinking abilities (transfer tasks) after the intervention.