Dear Carolyn: My son, 11, has been acting up in school: not doing his homework, talking during class, picking on younger kids, getting detentions and just being an all-around brat. At home, he's picking on his siblings and talking back to me and his dad.

We've had him tested by both his pediatrician and the school psychologist, and no underlying health issues of any kind have been identified.

Every other year, I take the children on a really big vacation. This year, we are going to California for three weeks. My son has never been and really wants to go. His father and I have told him all year that if he doesn't behave, he won't go to California. When I've reminded him, he behaves for a week or so, then goes back to misbehaving.

Best case, he will only have a 2.3 GPA at most, and we agreed on a 3.0 or higher for California. I told my son he won't be able to go, and he just laughed. My ex-husband and I decided we have to follow through.

Is it reasonable for me to leave him with his dad while I take the other children on vacation?

— Good to My Word?

Good to My Word?: He laughed. You have to follow through.

But, please, also learn from this that imposing big, abstract (to a child) consequences to immediate, impulsive acts is a serious mismatch of effect to cause and therefore likely ineffective.

Natural consequences — meaning, the bad outcomes you get in the moment, caused by the poor choice itself — are much better teachers than the stuff we make up. Canceling his trip puts months between action and consequence and makes you (in his mind), not his actions, the reason he’s missing out.

Plus, you always have to consider before imposing a consequence whether it’s something you actually want. You can’t say, for example, “No sports if you get a C!” when you know the sport is a healthy emotional outlet that helps your kid focus. If you’re caught up in the moment, it’s okay to say, “There will need to be a consequence, but I need to figure out what’s appropriate.” Then take time to see what you do and don’t want to impose and whether a natural consequence has already done the work for you — or whether you misguidedly stood in the way of such a consequence.

Given the seriousness of picking on other kids — “brat” is also cringe-inducing — it’s time to bring him, and you, and your whole methodology for raising him to a good family therapist. Something is going on, and defiance needs addressing ASAP, while you still hold whatever reins you still hold. When he’s 16-ish and can move about freely, you’re going to regret not figuring out how to secure his cooperation in his own well-being.

Learn what’s going on, and learn how to be a more effective parent. Try parenting classes, too. Soon, soon. Ask his pediatrician for suggestions, or PEP (pepparent.org).

Re: "Brat": My brother wore "brat" like a badge of honor and continued to escalate the bad acts that got my parents to give him the attention he needed. Please don't slander your child, and take Carolyn's advice to understand why he's feeling the need to act out.

— Anonymous

Write to Carolyn Hax at tellme@washpost.com. Get her column delivered to your inbox each morning at wapo.st/haxpost.