The incident took place at the Grove School in Market Drayton on Friday morning, with officers still at the school in the afternoon.
Police say "no threats were made to any pupils" but added that they had spoken to "a parent of a pupil from the school".
They also confirmed there have been no arrests in relation to the incident.
Pupils and staff were kept indoors during the incident, which took place around 11.30am.
Parents reported seeing police at the scene and being told that the school had been placed in 'lockdown'.
A spokesman for West Mercia Police said: "Police were called to the Grove School in Stafford Street in Market Drayton at 11.30am this morning following a report of a disturbance.
"Police are still in attendance and have spoken to a parent of a pupil from the school. No arrests have been made.
"As a precaution, staff and pupils remained indoors, although no threats were made to any pupils."