On Saturday and Sunday, PBS NewsHour Weekend airs excerpts from Time for School, a documentary that spotlights the global education crisis, coinciding with the U.N. summit, when world leaders take stock of the millions of children still left behind, despite the Millennium Promise of education for all. Since 2003, filmmakers have been following seven children in seven countries, many of whom have been struggling against the odds for a basic education. On Saturday, we meet Joab Onyando, who at 10 years old, starts first grade in a 70-student classroom without desks or chairs, in a school in Kibera, Nairobi's largest slum. Like millions in Kenya, he could not study at all until the government eliminated primary school fees in 2003. But Joab faces hardship at every turn. His mother dies. His father leaves. And Joab, who dreams of becoming an engineer, is forced to care for his two younger siblings, all while trying to stay in school.