Test-driven development (TDD) has garnered considerable attention in professional settings and has made some inroads into software engineering and computer science education. A series of leveled experiments were conducted with students in beginning undergraduate programming courses through upper-level undergraduate, graduate, and professional training courses. This paper reports that mature programmers who try TDD are more likely to choose TDD over a similar test-last approach. Additionally this research reveals differences in programmer acceptance of TDD between beginning programmers who were reluctant to adopt TDD and more mature programmers who were more willing to adopt TDD. Attention is given to confounding factors, and future studies aimed at resolving these factors are identified. Finally proposals are made to improve early programmer acceptance of TDD.