Hello there,hope you are doing well

there is nothing to worry dear.I am listing few tips kindly read them.

Find a quiet workspace away form other distractions and make it into your study space.

Pace. you can create a plan to study for 20 minutes, and then take a 5-minute break.

Simplify notes to few words. Then, on the test, it’s easy to expand on concepts.

Don’t keep re-reading the same notes. If they don’t make sense, you can  find other sources on the same topic to study from.

Now coming to your question,regarding concentrating in class all you can do is

1. Get a good night's sleep. Get at least eight hours of sleep each night. Set a bedtime routine, and go to bed at the same time each night. Your mind won't be able to concentrate if it's not rested...it needs a break, too!

2. Eat a healthy breakfast. Eating a nutritious meal in the morning gives you fresh energy for the day. Remember: a healthy breakfast doesn't mean a BIG breakfast. Just something nutritious and yummy to help you feel more energized and less groggy throughout the day.

3. Avoid sitting with friends. Chatting with friends isn't gonna give you the focus you need to stay on top of class. If you've got an assigned seat near a friend who wants to whisper with you all the time, ask your teacher about getting your seat moved and let your friend know that you just need to focus.

4. Get rid of any other distractions. Some of us get distracted very easily - and that's perfectly OK. But when distractions keep you from learning, that's a problem. Is that water bottle catching all your attention? Remove it from your desk. How about that gum you're chewing? Throw it out and start taking notes. Eliminate distractions (even if you don't want to) and you'll soon find your attention going to the teacher each class.

5. Look at the teacher and make eye contact. Your teacher is not just standing up there babbling - she's trying to give you an education! Show her that she has your full attention by looking her in the eye and observing her movements. Try your best to look alert. If you feel your eyes wandering to something else in the room, catch yourself and focus back on your teacher.

6. Know your goal. Most teachers tell you the subject of the class in the beginning. If possible, write it down the minute you hear it. What is it that needs to be done today? What will you be learning about? How can you stay alert and focused during this time? Set goals for yourself, and remind yourself of the objective throughout class. This way, you know exactly what you have to do.

7. Take notes. By taking accurate notes, you'll be able to "get into" the lesson. Recognize key points as your teacher speaks, and listen for key phrases such as, "This is important," "This is the main idea," "This will be on the test," etc. This can help you listen better; you'll have something to do and focus on.

9. Get involved in class discussions. When a teacher asks a question, offer to answer it. If she asks for an opinion, share yours. This shows the teacher that you're listening during the class, and that you know your stuff. It can also help you avoid those embarrassing moment when the teacher calls on someone and that student has no idea what they're being asked because they haven't been listening in class!

10. Ask a question. If you don't understand something, NEVER be afraid to ask. This really shows your teacher that you want to be better, and can recognize the things you're having a hard time with. Chances are, someone else in the class has the same question (and was too afraid to ask!). They'll be relieved - and so will you.

11. Do your best. When you walk into that classroom, put a smile on your face and some confidence in your step. Be the best that you can be at all times, and show your true potential!

Feel free to ask me in the comment box if you are having any further doubts

hope you find it helpful

Good Luck!