Welcome, from you question it may seem that this is your first time teaching 9 year-olds.

Well here are a few vital points to note; while you may be considering discipline, You’ll likely notice many behaviors in your tween that are common for their age group. That’s all part of their normal development. 9 year old’s face a variety of issues, ranging from hormonal changes and physical growth to social pressure and increased academic work

They typically exhibit the following behaviors:

• Fluctuating self-esteem
• Increasing awareness of how others perceive them
• Prefer to spend time with friends over family
• Become aware of their academic abilities
• Self-consciousness surrounding their developing bodies

Challenging behaviors can include:

• Becoming angry over seemingly small things
• Questioning and challenging authority
• Becoming argumentative and seeking out loopholes in your rules
• Misbehaving in order to fit in and impress friends
• Thinking they’re able to do everything on their own

Some recommended positive discipline strategies that effectively teach children to manage their behavior and keep them from harm while promoting healthy development includes:

1. Show and tell. Teach children right from wrong with calm words and actions. Model behaviors you would like to see in your children.
2. Set limits. Have clear and consistent rules your children can follow. Be sure to explain these rules in age-appropriate terms they can understand.
3. Give consequences. Calmly and firmly explain the consequences if they don’t behave. For example, tell her that if she does not work with peers she will sit in the class during recess/play break and won’t join her peers in play. Be prepared to follow through right away. Don’t give in by letting her go out to play after few minutes. But remember, never take away something your child truly needs, such as a meal.
4. Hear them out. Listening is important. Let your pupil finish the story before helping solve the problem. Watch for times when misbehavior has a pattern, like if your child is feeling jealous. Talk with your child about this rather than just giving consequences.
5. Give them your attention. The most powerful tool for effective discipline is attention—to reinforce good behaviors and discourage others. Remember, all children want attention.
6. Catch them being good. Children need to know when they do something bad–and when they do something good. Notice good behavior and point it out, praising success and good tries. Be specific (for example, “Wow, you did a good job putting that toy away!”).
7. Know when not to respond. As long as your child isn’t doing something dangerous and gets plenty of attention for good behavior, ignoring bad behavior can be an effective way of stopping it. Ignoring bad behavior can also teach children natural consequences of their actions. For example, if the child keeps refusing to write, she will soon realize that her whole academics depend on it and she may fail . If he misuses the swing and damages it, he will not be able to play with it. It will not be long before he learns not misuses the swing.
8. Be prepared for trouble. Plan ahead for situations when your child might have trouble behaving. Prepare them for upcoming activities and how you want them to behave.
9. Redirect bad behavior. Sometimes children misbehave because they are bored or don’t know any better. Find something else for your child to do.
10. Call a time-out. A time-out can be especially useful when a specific rule is broken. This discipline tool works best by warning children they will get a time out if they don’t stop, reminding them what they did wrong in as few words―and with as little emotion―as possible, and removing them from the situation for a pre-set length of time (1 minute per year of age is a good rule of thumb). With children who are at least 3 years old, you can try letting their children lead their own time-out instead of setting a timer. You can just say, “Go to time out and come back when you feel ready and in control.” This strategy, which can help the child learn and practice self-management skills, also works well for older children and teens.

​Spanking and Harsh Words are Harmful and Don’t Work. Here’s Why:
The AAP policy statement, “Effective Discipline to Raise Healthy Children,” highlights why it’s important to focus on teaching good behavior rather than punishing bad behavior.  Research shows that spanking, slapping and other forms of physical punishment don’t work well to correct a child’s behavior. The same holds true for yelling at or shaming a child. Beyond being ineffective, harsh physical and verbal punishments can also damage a child’s long-term physical and mental health.

• Spanking’s unhealthy cycle. The AAP advises that parents and caregivers should not spank or hit children. Instead of teaching responsibility and self-control, spanking often increases aggression and anger in children. A study of children born in 20 large U.S. cities found that families who used physical punishment got caught in a negative cycle: the more children were spanked, the more they later misbehaved, which prompted more spankings in response. Spanking’s effects may also be felt beyond the parent-child relationship. Because it teaches that causing someone pain is OK if you’re frustrated—even with those you love. Children who are spanked may be more likely to hit others when they don’t get what they want.
• Lasting marks. Physical punishment increases the risk of injury, especially in children under 18 months of age, and may leave other measurable marks on the brain and body. Children who are spanked show higher levels of hormones tied to toxic stress. Physical punishment may also affect brain development. One study found that young adults who were spanked repeatedly had less gray matter, the part of the brain involved with self-control, and performed lower on IQ tests as young adults than the control group.
• Verbal abuse: How words hurt. Yelling at children and using words to cause emotional pain or shame also has been found to be ineffective and harmful. Harsh verbal discipline, even by parents who are otherwise warm and loving, can lead to more misbehavior and mental health problems in children. Research shows that harsh verbal discipline, which becomes more common as children get older, may lead to more behavior problems and symptoms of depression in teens.

I hope this answers your questions?

Sources: Tween Discipline,  What’s the best way to discipline my child