Engelmann, S. (1980). Direct instruction. Educational Technology Publications.
Citazione stile Chigago Style (17a edizione)Engelmann, Siegfried. Direct Instruction. Englewood Cliffs, N.J: Educational Technology Publications, 1980.
Citatione MLA (9a ed.)Engelmann, Siegfried. Direct Instruction. Educational Technology Publications, 1980.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.