Police said no knives were found during the search at the Aldercar School in Langley Mill.
Letters were sent to parents and carers after the event to inform them of the search, which was organised by the Ripley Safer Neighbourhood Team.
Headmaster Tony Cooper said: "We did this as a proactive measure to ensure the health and safety of students."
The search involved about 800 students walking through a portable metal detector arch.
He added: "We are not naive - and we want to make sure that students, when they arrive on the site, are certain of their safety."
Insp Darren Roberts said: "The students were co-operative and feedback from the school was positive, with staff and pupils saying the searches made them feel safe."
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