Ghirmazion, who came to Germany from Eritrea at the age of 1, was allowed to enter the more advanced schools only against the vigorous opposition of his teachers, who advised him to remain with other immigrant students in the lower-standards schools.
A fifth of all migrant students drop out before earning their diplomas; the unemployment rate among migrants is double that of ethnic Germans.
"It's still expected from most immigrants who live here to behave as guests. That means to give up their own traditions and to assimilate," said Yilmaz Memisoglu, a 71-year-old retired electrical engineer who immigrated from Istanbul in 1961. He now is president of the Foreigners Advisory Council of Hesse.
"There were lots of hopes by the immigrants, especially with the talk about boosting German-language teaching and so on, but this election campaign has kind of spoiled all these hopes," Memisoglu said.
"Let me say one thing: Integration is possible only with confidence. And this confidence is gone."
At Thursday night's rally, more than 3,000 of Koch's supporters filled the square outside Frankfurt's ornate old opera house as a Dixieland band played the "Battle Hymn of the Republic." There were also at least 500 protesters, most of them young ethnic Germans, carrying banners reading "Anti-Fascist Action" and shouting "Nazis out!"
Koch, seemingly undeterred by his plunge in the polls, stayed on message.
"You yelling youths without any manners, you are not the majority here!" he proclaimed.
"We have to deal with the issues of integration and internal security, especially here in Frankfurt, where 66% of the children born have a migration background -- we have to talk about that," he said. "And when we see the problem of the violence, and when we see that immigrants are perpetrators of half the crimes, then we have to discuss these problems."
On stage with Koch was Merkel. The election is a litmus test for her awkward grand coalition in Berlin, which includes the Social Democrats. The chancellor opposes Turkey's bid to enter the European Union, and won applause at a recent party conference for saying that mosques should not be taller than churches.
Merkel has tried to calm the controversy, insisting that juvenile crime does not have a single ethnic dimension.
"It doesn't make sense to have a good public transport system if people don't want to use it after dark," she said at the rally. "Integration is a key issue for the future of this country. And at the same time, we have to talk about how to punish crimes like what happened in Munich."
Juergen Froehlich, a juvenile court judge, doesn't deny that a big proportion of those who pass through his courtroom are the children of recent arrivals. But deporting them is no answer, he says.
"The fact that we haven't managed to educate them into decent people doesn't mean it's the right thing to send them back to Turkey," he said. "They were infected here. And we have to heal them here."