Before joining a language school, many language learners ask whether the school provides a certificate. While most schools do provide certificates of attendance and level, it is better to separate the teaching and certification. Because bear for rare exceptions, school certificates aren’t recognized outside of the school premises. So their use is limited to being able to graduate to the next level of the course.
When a school certifies its students, there is a conflict of interest. It would look good on the school if many students score well in the examination. So the school would look better if it would make its ‘testing standards’ more lax. Besides, there are so many language schools in the world – how would any one certificate be able to get recognized by employers and universities.
So that’s why there are independent language tests, such as KLPT (Korean), JLPT (Japanese) IELTS / TOEFL (English), HSK / BCT (Mandarin), DELF/DALF (French), DELE (Spanish). These tests are recognized worldwide and translate readily into a the CEFR, meaning that the person you submit the certificate to can assess what you can and cannot do in the language.
So just like when you learn to drive, use your language school for instruction (like your driving instructor), and book a spot for recognized international certification (“practical driving examiner”) when you have reached a significant level and would like a certificate to prove it.
Many language schools can help you book your examination, and some even offer courses that prepares you for the type of questions asked. It’s good to make use of those if you can. But don’t rely on a school-issued certificate to open doors for you!