Why does someone study biology? Our most familiar reason is because someone is curious, or because they can acquire valuable skills and knowledge. This perspective is known today as ‘human capital theory'. While useful, it may not sufficiently explain individual student intentions, such as those of H.G. Wells (1866-1946). Most studied by historians of biology for his time in T.H. Huxley's teaching laboratory, it is less-well known that he got there only by doing well on Huxley's exams. For although Wells was curious, another central motivation for learning biology was to earn certificates and thereby advance himself. This paper therefore introduces credentialing theory to discuss H.G. Wells's early exam-taking, and then his exam-tutoring as a coach for the feared zoology exams of the University of London. By focusing not so much on knowledge as on its signs, credentialing theory reveals a tension between outer display and inner possession; plays up the importance of exams over curricular issues such as textbooks or labwork; and shows how people like Wells were keenly aware of the relative values of different certificates. The credentialing perspective gives us new insight into a world of "payment by results" in which it was assumed that teaching effectiveness was indicated by one's students' exam successes, and reveals a world of competitive exam coaches far less prestigious than the Cambridge Maths Tripos tutors written about by Andrew Warwick. Above all, we see how a relentless scepticism about whether signs of knowledge denoted its authentic possession led to repeated public outbursts about the dangers of 'cramming'.