A gypsum board corner assembly is formed with an integrated reinforcement strip. The strip may be a folded sheet-metal strip or a thin rod. First, a gypsum board is formed with a groove that extends substantially through the entire gypsum core, but leaves the laminate paper of one side. Then a reinforcement insert is placed in the groove. Here, the insert is formed of or includes ferromagnetic material. The insert is subjected to a magnetic field to pull the insert into the groove, by action of the magnet. After an amount of adhesive is applied in the groove, the gypsum board is folded along the groove while the insert is being pulled into the groove by the magnet. The resulting gypsum board corner assembly has a very accurately placed insert that defines a straight corner edge thereof.