I’ve watched parents raise children for 30 years (and raised four of my own), so I know how hard it is. Here, I share a question that came to me as a pediatrician, as well as my answer to this parent.

Dear Dr. Meg,
My three teenage daughters fight all the time. These fights tend to tear each one down, and in the end, their self-confidence is damaged. How can I teach them kindness, patience, and understanding at this difficult age?

Sincerely,
Parent of Three Fighters

Dear Parent of Three Fighters,
First, you must identify why your daughters are fighting.

Typically, there a are a few reasons siblings fight a lot:

1.) You.
I know that sounds harsh — but stick with me. Are you and your spouse yellers? Are you negative and stressed all of the time? Our children “wear our ills.” They soak up negativity from their surroundings. If this is the case, you’re in good shape. You simply need to effectively change the tone you set in your home.

Related: Why Daughters Need Their Dads So Much

2.) Jealousy.
Take a hard look at your daughters and see if you can find competition among them. Is one prettier, smarter, or more popular at school? Is one receiving more attention from you or your husband? Try to identify where one might be jealous of another and then deal with this. Point out each girl’s strengths and identify jealousy head-on. Tell the jealous one that the feeling is just a feeling and that it will eat her — and her alone — alive.

3.) Two-against-one attitude.
Do two routinely gang up on another? If one is always dumped on, then you must address this with the other two. Sometimes I find that two siblings routinely conspire against one sibling, and this is different from each equally criticizing the others.

Teach them how to have one another’s backs — this will help them bond.

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Once you know why your daughters are fighting, it’s time to fight the issue. Don’t do this by sitting all three girls down at once. Talk to them one at a time. If her father can accompany you, this is even better. When two parents carve time out to discuss an issue with a child, she knows that you mean business.

Begin the conversation by asking your daughter questions about herself. How is she doing? How is school? How are her friends? Then move on to the issue at hand. Tell her what you’ve seen. That you understand how hard it is to be a teenager and have siblings. And tell her you expect more from her, that she has to start being kind to her sisters.

And this is where it’s up to you to decide how you will respond to their behavior: through positive reinforcement or negative consequences. She either gets rewarded for being kind to her sister for a week, or she gets punished when she’s unkind. You know your kids well enough to know what they respond to best.

When you are finished explaining how you’re going to be tackling the fighting behavior from now on, she will be mad — and that’s OK. Tell her you are doing this because you are raising the bar on her behavior — and because you have full confidence that she can do better.

Related: The Gift of Self-Esteem This Christmas

Over the next few months, find ways your daughters can encourage one another. If one has a concert, tell the others that you want them to go and support their sister because she needs it. Keep rotating which sister needs help from the others and ask them to offer support because “that’s what sisters do.” In other words, teach them how to have one another’s backs and this will help them bond.

This will all take time, so be patient and don’t give up. Teaching our children to respect one another is a tough but crucial parenting skill. But it is worth it because if kids grow up to be nice to everyone but family members, they miss out on enjoying one of God’s greatest joys: family.

Dr. Meg Meeker has practiced pediatrics and adolescent medicine for 30 years. She is the author of the online course, “The 12 Principles of Raising Great Kids,” which is part of The Strong Parent Project.