I don't agree, I'd advise not to try Leiningen until you're comfortable enough with the parenthesis, the REPL and finish the koans themselves. This is 'getting your feet wet on Clojure', koans style. No need to introduce yet another tool when you're not dealing with the issues which Leinengen solves: managing library dependencies and configuration.

I remember I did: the koans first, then tried several exercises on the 4clojure website, then learned about Leinengen and only then I moved into 'projects'.