Complex sentence: While the Realschule is a selective school the "Erweiterte Realschule" is a non-selective school, that offers general education classes (that ressembles classes hold at the normal Realschule) as well as remedial classes.
Split into simpler sentences: While the Realschule is a selective school the "Erweiterte Realschule" is a non-selective school. It offers general education classes (that ressembles classes hold at the normal Realschule) as well as remedial classes.