The reaction of education providers to changing student markets has been to offer much more student centred approaches. Contemporary approaches have used the non-teaching time to offer a set of courses as summer school. Student involvement in summer school courses has been found to influence performance, acceptance at other schools, future careers, and interest in the subject. The main determinants of higher education enrolment appear to be social origin, cost and return expectations regarding employment and wages. Factors influencing students to enrol in summer school include reducing the number of semesters, and reducing class loads. In particular, business students were also found to enrol in summer school to make up for work and to graduate faster. Attempts have been made to forecast student enrolment intentions in summer school that are usually based on questionnaires. This study tests the forecast ability of questionnaires using business student responses. The results indicate there was a statistically significant difference between the questionnaire responses and the actual enrolment of those students. Questionnaires suffer from contamination issues so that questionnaire responses can be substantially different from the behaviour even with tertiary business students that may plan their enrolment. Thus, much research that uses questionnaire responses from students, and tertiary students as subjects to generalise to other situations lacks validity and is dubious.