A school zone refers to an area on a street

Street

A street is a paved public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable...

 near a school

School

A school is an institution designed for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is commonly compulsory. In these systems, students progress through a series of schools...

 or near a crosswalk leading to a school that has a likely presence of younger pedestrian

Pedestrian

A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

s. School zones generally have a reduced speed limit

Speed limit

Road speed limits are used in most countries to regulate the speed of road vehicles. Speed limits may define maximum , minimum or no speed limit and are normally indicated using a traffic sign...

 during certain hours.

Fines

Fines for speeding in school zones may be enhanced. For example, many authorities double speeding fines in school zones.
In NSW, there are increases in fines that apply in School Zones, during School zone times. The most common offences that occur in a school zone will also attract demerit points. This includes most parking offences, such as parking on a footpath / nature strip, double parking, disobeying a No Stopping or No Parking Sign and stopping in a bus zone.

When effective

School zone speed limits are often, but not always, only applicable during posted weekday hours near the beginning and ending of school when children are likely to cross roads. In some jurisdictions, the school zone speed limit is effective at all times when school is in session, plus additional time before and after the school day. Flashing amber lights often indicate when the school zone is effective. When a school zone also has a large playground

Playground

A playground or play area is a place with a specific design for children be able to play there. It may be indoors but is typically outdoors...

 facility, it may double as a playground zone and the speed limit could be in effect longer — or even continuously.

In California, school zones are generally in effect only "when children are outside or crossing the street" , and usually have a speed limit of 25 mph, or 40 km/h. School zone signs are sometimes amended with the notice "When children are present" (like shown on the photo) which emphasizes its definition in the drivers handbook.

School zones may also sometimes be in effect during school holidays, due to holiday programs that use school premises. In some locations however, school zone signs will be locked up during school holidays so that motorists can drive to the normal speed limit.

School zones typically have speed limits between 15 and 25 mph (25 and 40 km/h).

Overtaking moving or stationary vehicles in active school zones is prohibited in some jurisdictions.

Effectiveness

In a review of the available research, the Committee for Guidance on Setting and Enforcing Speed Limits of the Transportation Research Board

Transportation Research Board

The Transportation Research Board is a division of the National Research Council, which serves as an independent adviser to the President, the Congress and federal agencies on scientific and technical questions of national importance...

, part of the United States National Research Council

United States National Research Council

The National Research Council of the USA is the working arm of the United States National Academies, carrying out most of the studies done in their names.The National Academies include:* National Academy of Sciences...

, stated: