Koh Tao is well known of its beginner friendly diving. There are plenty on shallow reefs and easy bays where it is safe and easy to learn how to dive.
"Had a great week diving in Koh Tao with KTD. I really liked that KTD is purposely a small dive operator, unlike some of the very large groups on the island. A very personal touch. They are all about the customer and catering for their particular needs. I was just a reasonably experienced fun diver rather than doing a course and because there are rarely more than four divers with an instructor/guide, we were able to go to really quite spots. Above all, KTD are organised, but relaxed, and safety is number one. Their staff, both on shore and in the water highly skilled and knowledgeable, and just love diving. I have dived in Australia, Borneo and the Solomon Islands, but KTD stand out."