The CELTA is often described by graduates as the most rigorous and rewarding course they've ever done. Trainees put in a lot of hours each day into planning lessons, teaching, writing assignments and participating in class, which means they often have to put their social life aside so they can dedicate full days to achieving everything the CELTA expects of them. Despite the demanding schedule, trainees also say they've never learned so much in such a short period of time. No doubt, it's a full-on experience that shouldn't be taken lightly. 100% attendance is required and you're not just a student - you're a teacher trying out what you learn, as well.
That said, the support you receive on the course is unlike any other course you've taken in high school or college. The trainer-to-trainee ratio is 1 to 6 (maximum), so you will have a great deal of help from your trainer at all times. In general, you will get out of the course what you put into it.