Summer vacations interrupt the rhythm oflearning and may result in a loss of knowledge and skills. This studyinvestigates summer learning losses in an Austrian sample with nine-week summervacations. The results show losses as well as gains for students in lowersecondary education (182 students between 10 and 12 years old). Studentsexperienced losses in arithmetic problem solving (measured by the HAWIK IVintelligence test) and spelling (measured by the standardized spelling test HSP 5-9), but gains in reading (measured by the SalzburgReading-Screening, SLS-8).Losses or gains in a knowledge domain appear to depend on the degree ofpractice during the summer vacation. Contrary to American studies, studentscould make up for their losses within nine weeks following the re-start ofschool. In addition, socio-economic variables such as the mother's educationalbackground had a small impact on summer learning losses in arithmetic problemsolving.