Flames began spreading through a classroom at First Unitarian Cooperative Preschool in the 4100 block of Front Street shortly before 12:30 a.m., according to the San Diego Fire-Rescue Department.
It took crews about 15 minutes to extinguish the blaze, SDFRD spokesman Maurice Luque said.
The monetary losses were set at $300,000 to the structure and $150,000 to contents. The cause remained under investigation this afternoon.
On Jan. 6, a predawn arson fire caused an estimated $100,000 in damage to the school. No suspects have been identified or arrests made in connection with the crime, Luque said.