The resident reported seeing the large cat at about 12:20 p.m. near a vacant lot on Martin Avenue toward the rear of the elementary school, police said.
Officers went to the area to look for the mountain lion, but didn't find it.
A Pleasanton police officer said today there have been no additional sightings and no reports of mountain lions preying on pets or causing other disturbances.
While mountain lion sightings are rare, they happen from time to time because of the city's rural surroundings, police said.
Myla Grasso, public information officer for the Pleasanton Unified School District, said there have been several mountain lion sightings in the area over the years.
Mohr Elementary School is near a quarry and a there is a large open space area to the south and east, which is home to many types of wildlife.
When credible mountain lion sightings are reported, the school district often sends letters home to parents reminding them of safety precautions they can take, Grasso said.
Tuesday's sighting, however, is not a cause for alarm, she said, and no mountain lion has ever approached children at the school.