"Object-Oriented Programming" subject is included in the ACM Curriculum Guidelines for Undergraduate and Graduate Degree Programs in Computer Science as well as in Curriculum for K-12 Computer Science. In a few research studies learning problems and difficulties have been recorded, and therefore, specific pedagogical guidelines and educational tools have been proposed which aim at better supporting the instructional process of Object-Oriented Programming. This paper presents an empirical pilot study of a seminar related to the basic principles-concepts of Object-Oriented Programming. The seminar was at undergraduate educational level using the Java language and web technologies. Its instructional approach was based on selected best instructional practices (either in the form of guidelines or design patterns) already published in the literature. The fundamental aim of the present study was to investigate the factors that might affect the learning effectiveness of a web-enhanced instructional process of the Object-Oriented Programming subject. (Contains 4 tables and 6 figures.)