Why not use IWB for testing?

Scott Thornbury (2009) points to studies in which the students benefited from use of  IWB in classroom instruction  and where the teachers involved expected the use of the IWB to improve students test scores but where there were no significant differences in the students’ test scores. The students were instructed with the aid of the IWB but tested in the traditional way. I wonder if there would have been a difference if they were tested using the IWB. With so much interest and expectation generated from IWB instruction why not use it to administer the test and see if there is any impact?