Undated (AP) _ More than 25,000 youngsters in Boston had to find alternate ways to get to classes today because of a walkout by school bus drivers, while teacher strikes continued in seven states, disrupting education for 720,000 students.

Hundreds of striking teachers reportedly crossed picket lines in Chicago on Thursday, while teachers in two Michigan districts returned to work and representatives of striking teachers in Detroit reported no progress in negotiations.

In Chicago, 332 of the more than 28,000 striking teachers reported for work Thursday to attend seminars and plan courses, Ken Masson, a spokesman for the Board of Education said today. He did not know today's turnout.

''I think you don't set a very good example as far as being good citizens to your children by going out on strike,'' said Ann Patricia Duffy, a junior high teacher.

Teachers in their fourth day today of their walkout against the nation's third-largest school district want a 15 percent salary increase over two years, but the school board says it can't afford it.

Federal mediators broke off negotiations Tuesday and new talks were planned for Saturday. Many of the 430,000 public school students have been sent to alternative programs set up by city and private agencies.

''We hope ... the board has given some new directions to its negotiating team,'' union spokesman Chuck Burdeen said late Thursday.

The board contends the strike is illegal because the Chicago Teachers Union erred by filing a strike notice before the start of mediation.

The union, however, accused school officials of bad-faith bargaining following the leak of a memo saying the board could save $7.5 million if that strike lasted 16 days.

In Massachusetts, a judge ordered 370 striking teachers in Revere on Thursday to end a two-day strike. School officials were keeping classes open for the system's 4,600 students.

In Seekonk, 149 teachers voted to strike today and shut down five schools attended by 2,300 students.

Talks resumed Thursday evening to settle the Boston strike by school bus drivers seeking higher wages from three companies. Their action forced more than 20,000 children in grades 1 through 9 to seek alternate transportation on their first day of classes. High schools opened today, and up to 27,000 of the city's 56,000 pupils could be affected by the strike. Today's attendance figures in Boston were not immediately available.

In Michigan, classes in Marquette resumed today for 4,830 students, the Michigan Education Association announced. The district's 270 teachers had reached a settlement earlier but remained on strike until an accord was reached with 142 support employees, the union said.

Negotiations broke off Thursday in the effort to settle the Detroit strike, which began Aug. 31. That walkout and seven others around the state idled 12,530 teachers and 211,340 students.

Bargainers representing the teachers and the school board resumed negotiations today, according to a spokeswoman for the Detroit Federation of Teachers, who declined to be identified.

A hearing also was held Thursday before a Wayne County Circuit judge on the school board's request for a back-to-work order, said teachers' union spokeswoman Lois Vagnozzi. The judge took the request under advisement, and told both sides to resume bargaining.

The Detroit school board has abandoned its demand that teachers accept a wage freeze, said board member Rose Mary Osborne. But she said the district needed new money to be able to afford to pay its teachers more.

In Mount Clemens, a judge ordered bargainers to meet around the clock until they reach a settlement. The district's 221 teachers struck Aug. 31, idling 3,086 students.

Bargaining sessions in Ohio's Youngstown, North Ridgeville and Berkshire districts ended in frustration for striking teachers.

In Youngstown, Superintendent Emanuel N. Catsoules canceled the start of school Thursday after only 2,400 of 15,500 students attended classes on the first day of the walkout Wednesday. Schools remained closed today.

Hopes for an end to a 10-day strike in North Ridgeville were dashed when teachers voted to reject a tentative offer from the school board.

After a one-day walkout, teachers voted Thursday to return to work in Pennsylvania's 2,100-student Western Wayne County School District, but more than 18,000 students in six other districts were kept out of school as strikes continued.

Also on strike were teachers in Edmonds, Wash., idling 17,500 students, and in Elizabeth, N.J., where 15,000 children attend classes.