Compulsory school attendance ("Schulpflicht") in Germany requires that all children between the ages of six and eighteen attend school. The German general school system has two stages of school education: primary and secondary. Primary education runs from years 1 to 4. Secondary education ("Sekundarstufe I") runs from years 5 to 10 with three different tracks of schooling: Hauptschule, Realschule (in Lower Saxony, these two tracks are combined into Oberschulen) and Gymnasium. Students receive an intermediate-level qualification once they have successfully completed year 10. Students who are eligible to take Abitur exams continue secondary education until year 13 ("Sekundarstufe II"). The German school system also has Gesamtschulen (GS) and Integrierte Gesamtschulen (IGS). These schools combine all three tracks of schooling and allocate students to different course levels according to performance: remedial, basic, and advanced. Kooperative Gesamtschulen (KGS), on the other hand, keep the three tracks of schooling separate and teach students separately even though they all attend the same school.
As each federal state has its own school holiday dates, the school year starts in either August or September. In the past, part-time education was more common in Germany than full-time education, with the school day ending early, between 13:00 and 14:00. In recent years, however, full-time education has become increasingly prevalent and many schools now offer full-time education until 15:00 or 16:00 and provide lunch at cafeterias and/or dining halls ("Mensas").
Most schools in Germany are public and do not charge tuition. Parents do, however, have to pay for learning materials and school trips and outings. Private schools are less common in Germany.
The Amt für Schule und Bildung of the City of Oldenburg is responsible for schooling and education and informs on the various schools in Oldenburg. You can consult the school administration ("Schulleitung") and go and see the schools for yourself before choosing one for your children.