Reds manager Keith Hill says he played winger Reuben Noble-Lazarus at left-back at Crewe on Tuesday to teach the 18-year-old a lesson.
Noble-Lazarus is the youngest ever Barnsley player and has scored once in 20 games for the Reds.
Hill said: “I wanted to get Reuben to realise that there is a physical impact in football. I played him up against Mathias Pogba who is a big, strong, powerful winger. I wanted to show Reuben what kind of impact a wide player can have on a full-back.
“It was sink or swim for Reuben and, although he struggled at first, I was impressed with how he started working things out on his own.”