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Berlino Schule
Each month they offer a free trial lesson where you can try out a class before you part with your hard earned money. Price wise, they are one of the cheapest in Berlin at 192 € for a four week intensive course of 48 teaching units.
In addition to German classes, Berlino also offers English and Italian as well as other workshops like Photography, Film-making, singing or acting, and also sponsor film nights which are available to students at discounted rates.