This article describes research on the learning of object-oriented programming (OOP) by novices. During two academic years, we taught OOP to high school students, using Java and BlueJ. Our approach to teaching featured: objects-first, teaching composed classes relatively early, deferring the teaching of main methods, and focusing on class structure before algorithms. The research used a constructivist qualitative research methodology using observations and field notes, audio and video recordings, and an analysis of artifacts such as homework assignments. The findings were divided into four primary categories: class vs. object, instantiation and constructors, simple vs. composed classes, and program flow. In total, 58 conceptions and difficulties were identified. Nevertheless, at the end of the courses, the students understood the basic principles of OOP. The two main contributions of this research are: (i) the breadth and depth of its investigation into the concepts held by novices studying OOP, and (ii) the nature of the constructivist qualitative research methodology. (Contains 4 notes and 1 figure.)