Some of the things that you learn in your Spanish language immersion classes would be the correct tones and voice inflections to be using while you are talking. You can rest assured that this is 100% first language speaker Spanish that you are using. You will actually be instructed in how these people speak on a daily basis.
Also, your comprehension is going to get so much better because with no English and no translation methods to fall back on, you are simply forced to be able to listen and to understand what is going on. You will never learn to speak a language better than you will if you are learning by Spanish Language Immersion, and that is a proven fact.