Pupils were able to leave the premises safely at the end of the school day and the injured person had since been discharged from hospital, the spokesperson said.
Supt Paul Ferguson, from South Yorkshire Police, said: “We understand this incident will have caused significant concern in the local community, especially for families who had children in school at the time.”
Officers would remain in the area carrying out “intensive, high visibility patrols” and inquiries would continue through the evening and into tomorrow, Ferguson said.
“We will continue to work closely with the school and key partners to ensure the school is a safe and welcoming environment.”
Ferguson said officers would remain in the area and continue to support the school and local community on Friday.