[plt-scheme] automarking again

Still trying to figure out how to script automarking of student 
submissions. Suppose they are using Beginning Student. Their submission, 
with embedded tests, designed to be run in DrScheme, is in student.ss. 
Our tests of their functions, using printf to display the results, are 
in tests.ss. I write a module which exports printf, called io.ss. Then I 
say:

mzscheme -e '(require (lib "htdp-beginner.ss" "lang"))' -vmf student.ss 
-t io.ss -f tests.ss

and it complains that I have definitions in the Interactions window when 
they should be in the Definitions window. If I change "beginner" to 
"intermediate", this works. Any suggestions?

(I am not convinced that I am loading Beginning Student the right way.)

Many thanks. --PR