Complex sentence: Adolf Fredriks Musikklasser is a high-profile grundskola (general junior high school) in Stockholm, Sweden, was founded in 1939 to offer musical children in Stockholm the opportunity to extend their studies by extra music and choral training.
Split into simpler sentences: Adolf Fredriks Musikklasser is a high-profile general junior high school (Swedish: "grundskola") in Stockholm, Sweden. The school was founded in 1939 to offer musical children in Stockholm the opportunity to extend their studies by extra music and choral training.