"I don't want you to make the same mistakes I did!"
Have you heard this parental lament when it comes to school? What kind of mistakes do you want kids to make? Clamp down on them too hard and watch them take it to the next level.
Instead of provoking a game of one-upmanship, allow exactly those same (non-life-threatening) mistakes, the ones we all learn from. Allow them early and often without shame. Young people will figure their own ways out and be more likely to ask for help when they can't.
The less big a deal you make of a rhythm of academic underperformance, the more receptive they will be to accepting suggestions and help to change it the next time around. Focus less on having fallen off the horse and more on how to get back on.
And if they don't care? Find out what they do care about and take it from there. Partnership works better than dominance.