I can't speak for the conditions in Brazil. However, from my own experiences in Japan and from talking to people in other countries, teaching privately usually doubles your pay. Uni teachers get a fair(er) coin, but private conversation schools really don't pay all that well. There are advantages and disadvantages, though.
1. A conversation school gives you a solid chunk of hours each week with reliable pay.
2. A conversation school (hopefully) offers training and advice, which helps you improve.
3. A conversation school lets you talk with colleagues and trade ideas and knowledge.
4. A conversation school gives you paid vacation time.
I supplement my pay with private lessons, because it's a lot of work to live solely off those private lessons. Students come and go, cancel lessons, etc. Those private students also can't meet at my convenience, one after another, so there may be a four hour break in the middle of the day with absolutely nothing to do.
In short, don't be surprised that private lessons pay double, or that the standard pay at a school is so low. You see the same just about everywhere.
Hope this helps.
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