From SF Bike Coalition:

New this year, Bike to School will be celebrated across a full week! Over 2,500 youth and adults at 40+ pre-K through high school campuses will participate in the joys and many benefits of biking to school. The week is sponsored by the San Francisco Safe Routes to School Partnership and organized by the San Francisco Bicycle Coalition.

For more details and to find out what day your school is celebrating, click here