What is "hogstadium"

Högstadium ("high-stadium" or "upper stage") is a Swedish former term for the seventh to ninth grade (grundskola) of the Swedish school system. Since 1994, it is no longer in official use, but is still used informally. After högstadiet, there is no compulsory school attendance; however, most Swedish students go on to the gymnasium for three more years of studies. The term was also used for grades 7-9 in Finland from the 1970's and up to 1999.