Unions said that the demonstration, backed by both left wing and right wing opposition parties, drew 120,000 people, or about 80 percent of the teaching profession, according to local press estimates.
A protest in Lisbon in March was attended by 100,000 people.
The teachers were demonstrating against reforms that took effect with the current school year, in particular new procedures for assessments required for promotion.
These take into account results obtained by teachers' pupils and according to the teachers increase their workload.
They are also unhappy about new timetables. Unions say there will be protests in regional capitals at the end of the month and a national day-long strike in January.