I’d rather steer a student into a challenge than away from one. I think we should be honest with kids about the challenges ahead of them, but we should also be encouraging them to rise and grow to meet those challenges, not to flee from them.
e.g. “Pre-med will be extremely difficult if you continue at your current level of performance. It’s a gauntlet designed to weed out many students. It is often graded on an unforgiving curve. Unless you bring your absolute best, it is YOU who will be weeded out. So bring it! Bring your best!”
Some kids just ramp up slower. Some kids tank high school on purpose because they are bored (I was one). Some kids are very T-shaped (academic talent strongly focused in one particular area), which works poorly in high school and much more effectively in college.
I wouldn’t steer those kids at all, but I would tell them all I can about the road they are driving on.