By diligent service he won the esteem of Mr. Beyerbach, and devoted his leisure to self-improvement, taking private lessons in mathematics and physics, and attending the lectures of Professor R. Bottger on mechanics at the Trade School. When his apprenticeship ended he attended the Institute of Dr. Poppe, in Frankfort, and as neither history nor geography was taught there, several of the students agreed to instruct each other in these subjects. Reis undertook geography, and believed he had found his true vocation in the art of teaching. He also became a member of the Physical Society of Frankfort.

In 1855 he completed his year of military service at Cassel, then returned to Frankfort to qualify himself as a teacher of mathematics and science in the schools by means of private study and public lectures. His intention was to finish his training at the University of Heidelberg, but in the spring of 1858 he visited his old friend and master, Hofrath Garnier, who offered him a post in Garnier's Institute. In the autumn of 1855 he removed to Friedrichsdorf, to begin his new career, and in September following he took a wife and settled down.