On Monday, hundreds of students at Tehran University demonstrated, causing President Mahmoud Ahmadinejad to cancel his visit there. On Sunday, students held a smaller protest outside the philosophy department building of Tehran University, where a member of Parliament, Gholam Ali Hadad Adel, gave a speech.

The student protests were the first of the new school year, which began last week, and took place despite the arrests of dozens of student leaders around the country this summer and increased pressure on others not to demonstrate.

Several influential university professors and former student leaders have also been jailed since June. Dozens of student activists have been jailed this month or barred from attending classes, according to student Web sites, in an effort to intimidate students.

The absence of student leaders suggested that the demonstrations were spontaneous, analysts said.

“Student leaders do not have a formal presence,” said Ali Afshari, a former student leader who is currently in Washington and is still in touch with students in Iran. “They have all been summoned and threatened. But the frustration is very widespread and the government can only shut down the universities if it wants to stop the protests.”

The protest movement, which has produced some of the nation’s worst unrest in 30 years, emerged as a response to a widespread belief that Mr. Ahmadinejad falsified election results in his favor. Universities have often been the site of protests, partly because of a student pro-democracy network, the Office for Consolidating Unity, and a law that bars police officers from entering campuses.