Complex sentence: Summerhill School arose out of the International School in Hellerau, which in early 1924 moved to Sonntagsberg in Austria, and in late 1924 to Lyme Regis in England, where it acquired the name Summerhill.
Split into simpler sentences: Summerhill School arose out of the International School in Hellerau. It later moved to Sonntagberg in Austria, and in 1923 to Lyme Regis in England, where it acquired the name Summerhill.