Here is the list of Clojure Koans Resources collected from the web. It is not exhaustive by any means, feel free to add comments of your own.

Clojure Koans are a free set of programming exercises for learning the Clojure programming language. Many will find Clojure quite different from any programming language they've used before. The koans' incremental, interactive approach to learning the language will help make the transition feel natural.

4Clojure is a resource to help fledgling clojurians learn the language through interactive problems. The first few problems are easy enough that even someone with no prior experience should find the learning curve forgiving.

Clojure Koans Walkthrough is another free set of programming exercises for learning the Clojure programming language. This uses Light Table IDE created by Chris Granger.

Exercism helps in improving skills. It provides support to various languages including clojure. There set of instructions for using exercism is available here .

Using Project Euler problems as small projects bridges the gap because they usually can be solved with simple language basics & yet you can rewrite them in more elegant ways as you advance. Also, as literally hundreds of solutions are available on the net in various languages you can compare your new language’s capabilities and style with other languages you already know.