Where I grew up in NY, the speed limit applied during all school hours when the lights on the sign were flashing, usually 7AM-3PM. Make sure you always drive slowly and carefully near schools, residential areas, parks and playgrounds: children may suddenly run into the street.

In San Diego, CA, school speed limits only apply if children are present. Oftentimes, school zone signs have the “When children are present” notice. In Colorado, school zones are (supposed to be) marked with a sign at the beginning and at the end of the school zone. A typical school zone speed limit in most US states is between 15 mph and 25 mph (25 and 40 km/h) unless otherwise posted. When the school sign is posted "School Zone - 25 MPH when children are present," does this mean you can go the speed limit e.g.