In my corner of the educational wilderness, which is admittedly a "special" one, it's my job to structure tasks so that students can succeed 80% of the time if they make a reasonable effort. When they get closer to 90%, the bar gets raised. If they're playing around, I'm free to call them on it. If they're really trying and not succeeding, I have to change the task, usually with student input, but then I'm free to lean on them. There isn't much red ink (actually, I use bright green) but they do see my comments put into the session log on the computer, which can be pretty motivating when it's something like the following: "Everyone finished except Jessica Goof-off."