Big Nerd's Ranch ( https://www.bignerdranch.com/ ) especialy for mobile app development. Their bootcamp is called "retreat", and they also work as developers and publish books.
tl;dr: Big Nerd Ranch offers short retreats for intermediate and advanced instructors. They are not cheap but they are thorough and powerful, as long as you're willing to put in the work.
Details: We have short (typically 5 day), intensive courses. The instructor leads the class through a series of lectures and intense labs, building out real applications throughout the week. The instructor works with each student to help them maximize what they can learn and achieve during the week.
There is no magic for scaling across different ability levels, but there are ways to do this better or worse. Our courses target intermediate to advanced level learners. We intentionally build our chapters, demonstrations, and lectures to be very dense with material. For the advanced students, they're able to glean API gotchas and sharp corners, as well as real world tips (pretty much all our instructors are also active consulting developers), and lots of looks at different working practices. Seeing another developer work is a great way to learn new techniques.
For intermediate or closer to beginner students, they won't that level of detail as much, as they're still absorbing all the new APIs, design patterns, and details necessary to just get apps building and shipping.
Our courses allow you to get out what you put in. In other words, there's not any particular magic to leveling up. You have to put in the hard work yourself. But I believe our retreat-style approach - where we remove or take care of all possible distractions, and provide expert aid at your call - gives you the best chance to maximize how much you can learn in a week. Food and lodging is included. You'll spend the week learning, programming, and going for hikes every day. It's sort of my ideal world. :D
We don't call them bootcamps half-heartedly. You'll be exhausted by Friday. But if we've done our job right, you'll feel like you've just shortcut several months of work in leveling up as a developer.