If you want to learn how to surf, you are going to need a very good private instructor for surfing lessons. More importantly, you definitely need to hire a private instructor (i.e., one-on-one teacher/student ratio). Here are all the reasons why you should be your instructor's only student during your scheduled lesson time.
You Are Attempting to Learn a Complicated Sport
Surfing requires you to learn how to paddle out to sea while sitting on a board that is only about a foot wide, and then recognizing when you are at just the right spot and jumping up to put both feet on the board to ride into and with the oncoming waves. This is not something you want to try to learn from an instructor whose attention is split between you and other students. You want the instructor's full attention in order to spot you and see what you are doing incorrectly and help you fix it in the moment. If you got into a jam and fell off your board, you also want to know that someone is there to rescue you and help you grab onto your board before it gets too far for you to reach on the incoming waves. (You will be tethered to your board, but the tether is rather long, and your board can still drift some distance from you.)
You Want to Know That Your Instructor Has Your Back
Surfing is a sport that requires that you do it with a buddy. You and the buddy watch for each other to make sure you do not drown, are not attacked by sharks, and do not end up in a riptide or undertow of a very large wave. Professional surfers may attempt to skip the buddy system sometimes, but even they know that it is safer to surf in pairs. Because you are just learning to surf, it is better to have the instructor all to yourself so that the instructor is your "buddy" when you are attempting to ride a wave. In this capacity, the instructor not only provides you with surfing instruction but also with safety and security.
There Are Unseen Dangers in the Water That Your Instructor Knows How to Spot
Your instructor usually knows how to address jellyfish stings, spot a shark in the water, and watch for other dangers that you are probably not familiar with because you have never surfed. You will learn how to handle these issues, but hopefully, you will never have to face them. If your instructor only has you in a private lesson and no other students, he/she can focus on watching the water around you as you attempt to surf.