Introductory object-oriented programming is considered difficult to teach and a number of different methodologies have been proposed, such as using graphical user interfaces (GUI's). The GUI methodology as reported in the literature is mostly evaluated using a qualitative assessment through the use of student feedback. In contrast, this paper reports on a quantitative study for this methodology so as to provide a more complete evaluation of this teaching approach. The research question for this study is as follows. Is there any difference in learning outcomes between the control group and the test group? Quantitative data was collected from the final exams of each group. The same five multiple choice questions and one open question were placed on the final exam for each group, and the results of the exam questions were statistically analyzed and compared. The results show that there was no negative result using GUI's as a basis for teaching object oriented programming.