LOS ANGELES — School buses have continued operating as district schools were kept open here despite the start of a teacher strike on Monday.

About 8,560 Los Angeles Unified School District students rode their buses to school, according to a news release from the district on Monday, representing about 40% of the district’s average daily ridership. Schools in the nation’s second-largest district were kept open with a skeleton crew of substitute staff members, the Associated Press reports. (The district’s school bus fleet has a total of 1,763 route buses and contracts out 633 buses, typically transporting more than 100,000 students daily, according to SBF’s Top 100 School District Fleets list.)

Los Angeles Unified School District principals reported providing instruction to approximately 141,631 students at 1,240 schools, according to the district’s Facebook page, though that number is incomplete, since 54 schools still had to submit reports as of late Monday afternoon.

United Teachers Los Angeles reported on its Facebook page that 30,000 union members participated in the strike on Monday. Charter school teachers are joining the strike as it continues into Tuesday, marking this as the first charter teacher strike in California according to the union.

Mainly at issue in the strike are class sizes, the hiring of additional staff members such as nurses, counselors, and librarians, and a 6.5% raise for teachers, according to National Public Radio. This is the first time in nearly 30 years that teachers in Los Angeles have gone on strike, according to the news source.