The self-study classes in the school are more formal and the learning effect is better. However, there are not many schools offering self-study classes, many of which are full-time. They can take classes with students at school, but they are not suitable for people who work.
There are many kinds of self-study classes, face-to-face teaching and video teaching in society. You can study in your spare time without delaying your normal work. The disadvantage is that the teaching quality is difficult to guarantee. Some remedial classes are better and some are not so good, so you need to be clear about yourself.