Throughout my career, I have met a lot of people interested in learning foreign languages. Each one have told me which method or technique have been more useful for them during their language learning process. However, despite having different opinions, all of them coincide in one point: the language classes made up for five or more students hinder your language learning.
The big advantage to attend at school is to be in contact with a native speak who is a qualificated teacher who can guide you thoughout your learning process. Nevertheless, if one class if made up for many students, your contact with your teacher declines. In that way, neither you will receive a specific attention in order to solve your language mistakes, nor you will have the chance of speaking directly with a native speaker in your target language.
In the other hand, a class made up for many students can be rewarding. Being in contact with other people with whom you share the same aims (learning a foreign language) can provide you an special motivation. Besides, you can share experiences, meet new people, and get in contact with new cultures and new social and language factors that were unknown for you before.
In summary, all it's up to you. Learning a foreign language is, normally, a free trip that we choose freely. Therefore, you are responsible for learning a language in the way you prefer.