This article describes the Swedish initiative of municipal technology centres from a gender point of view. These centres provide after-school technology education for children aged 6-16. By means of an ethnographic study, the effects of the use of single-sex groups in increasing the interest of girls and boys in technical activities have been studied at one of the centres. The importance of the gender of the teacher relative to the gender of the pupils is also considered. The results show that single-sex groups meant different things to boys and girls, and that the teachers' way of "doing" femininity and masculinity, respectively, in the different groups was of some importance. The results indicate that single-sex groups alone do not break down gender barriers. However, there are lessons to be learnt from a leisure-time activity that provides a different setting from that of single-sex science education in ordinary schooling. (Contains 2 notes.)