Try Again by Oliver Optic

The next evening Harry was conscious of having gained a little in the ability to discharge his novel duties. Either the partners and the clerks had become tired of swearing and laughing at him, or he had made a decided improvement, for less fault was found with him, and his position was much more satisfactory. With a light heart he put up the shutters; for though he was very much fatigued, the prestige of future success was so cheering that he scarcely heeded his weary, aching limbs.

Every day was an improvement on the preceding day, and before the week was out Harry found himself quite at home in his new occupation. He was never a moment behind the time at which he was required to be at the store in the morning. This promptness was specially noted by the partners; for when they came to their business in the morning they found the store well warmed, the floor nicely swept, and everything put in order.