Three of Joseph Romano's students at Bishop Canevin High School made the 270-pound piece of chalk using plaster of Paris and 14 gallons of water they mixed together in a 32-gallon trash can.
Chalk is typically made from gypsum, but can also be made using plaster of Paris and water, which the boys mixed for 15 minutes then let set for three days before it dried.
Romano is giving extra credit points to Nick Sylvester, of Kennedy Township; Matt Durbin, of Robinson Township; and Terry Dougherty, of Crafton.
Romano says he'll probably chip off smaller pieces of the chalk to use in his classroom.
