The incident took place on Wednesday, (December 6) and was reported to Lincolnshire Police straight away.
Adam McDermott, Regional Projects Officer for Wellspring Academy Trust said: “This was an unpleasant and terrifying experience for our pupils, especially those of primary school age.
“If anyone show anything and has any information, then please contact the police.”
The site is currently under consultation to become one of four new free schools in the Lincolnshire area.
But Mr McDermott has also said that this consultation has now been extended until Sunday, December 31 to give residents more time to give their feedback.
If you would like to put forward your views during the consultation period, you can either email the Academy Trust via: [email protected]
Or you can complete the online questionnaire - https://www.surveymonkey.co.uk/r/XRZJDQ3 or complete the questionnaire on the leaflet and post to: Wellspring Academy Trust, Digital Media Centre, County Way, Barnsley, S70 2JW.