Lisps have been used continuously for university level introductory programming courses at least since MIT's 6.001 in the 1980's. Today, PLT (the group responsible for Racket) might be considered to be the leader in research into the pedagogy of computer programming and Felleisen's How to Design Programs and student language sequence are used by several schools. I believe they include Rice, University of British Columbia, Brown, and Felleisen's Northeastern University.
At my bachelor university (University of Bologna, Italy) we used to have Scheme with htdp for the programming 101 course. That's what I did when I studied there but apparently now they (unfortunately) changed it to C++. The day I found that out was a very sad day for me.
Funnily enough, the PLT group is working on a new language for education called Pyret http://www.pyret.org/. It's not very similar to Scheme, it is very similar to Python.
It would be more accurate to say that that Shriram Krishnamurthi and his group at Brown, which are one part of the large PLT "collective", are working on Pyret. The rest of us are still working on Racket.
The PLT Group's homepage: http://www.ccs.neu.edu/racket/