to become a schoolteacher, a police officer, or a soldier. Most jobs, however, do not require German citizenship. Those who do not hold German citizenship but instead just a "right to reside" may still receive many social benefits. They may attend schools, receive medical insurance, be paid children's benefits, receive welfare and housing assistance. In many cases guest workers integrated neatly into German society, in particular those from other European countries with a Christian background, even if they started out poor. For example, Dietrich Tränhardt researched this topic in relation to Spanish guest workers. While many Spanish that came to Germany were illiterate peasants, their offspring were academically successful (see: Academic achievement among different groups in Germany) and do well in the job market. Spanish were more likely to marry Germans, which could be considered an indicator of assimilation. According to a study in 2000, 81.2% of all Spanish or partly Spanish children in Germany were from a Spanish-German family. There were some, and still are, tensions in German society, because Muslim immigrants feel they have been religiously discriminated against. For example, while the Christian churches are allowed to collect church tax in Germany, Muslim mosques are not able to do so as they are not as yet organised in a cooperative association (which is sometimes criticised as forcing Christian organisation-style on non-Christians). While German universities have educated Jewish, Catholic and Protestant clerics and religious teachers, in the past none of the German universities have offered education for Muslim teachers and clerics. However, today such university courses exist. Muslims were often also not pleased to find the Christian cross displayed in German classrooms, something that at the time was relatively common. The fact that most schools offer Catholic and Protestant religious education and ethics but no Islamic religious education has also been criticised (especially because religious education is compulsory, replaceable by ethics). Students are allowed to wear a normal headscarf in school, however in 2010 a Muslim student sued a headmaster, because she was not allowed to wear a hijab in school. East Germany After the division of Germany into East and West in 1949, East Germany faced an acute labour shortage, mainly because of East Germans fleeing into the western zones occupied by the Allies; in 1966 the GDR (German Democratic Republic) signed its first guest worker contract with Poland. In contrast to the guest workers in West Germany,