I would think that good practice would discourage it, particularly for child users. The ADA standards require an accessible route from the boundary of the site to the accessible entrance (and to other accessible features, such as parking) but do not require the AR to be a sidewalk. Here's a thought: provide a wide sidewalk and allow the occasional car to use it to access the parking lot...

School traffic circles in many schools are some of the most heavily trafficked sites as parents and older siblings drop off students. If it is a High school, even worse, as many of the "parking lot" cars will be driven by young persons. Respectfully, please do not consider that option serving a school. Laura Williams, President,
Californians for Disability Rights, Inc.

California Building Code (Amended UBC) has a provision under "Hazards" for "Detectable warnings at hazardous vehicular areas." It states "If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning which is 36 inches wide . . ." The intent is clear - separarte pedestrian paths from vehicular circulation. At a school, this type of provision could not be more necessary.