All house dance classes are challenging. I've never been to one that's not. They're also a blast and a wonderful way to party early, sober. There are several studios in Berlin. I hoped to try them all and become a regular somewhere but never found a favorite. And to be honest, considering it's Berlin, I expected the music to be better.
Flying Steps Tuesday with Peeps (above)
This class is about DANCING. The class is influenced by salsa moves, teacher speaks in english french and german mix, hard to get into but is a lot of fun and a great work out. The music is ok, some unwelcomed pop tracks and no freestyle, there is a little dancing across the floor. There is a waitlist, so I highly recommend booking online a few days early.
D!'s Dance school: Monday at 19:00
This one is a bit technical. The music is better for people who like the more techno side of house music. This teacher focuses quite a bit on footwork and some on the soul of the music. The people in the class are not so expressive, but the end of the class ends with freestyle dancing and no choreographed dance. This teacher is clearly a house head and influenced by ballet. This class is taught in German.
I heard good things about the classes here but didn't get to try it myself. It's around the corner from Flying Steps.