As stated, it is possible it is a clerical error, but, it is also possible that the needed someone to work those times and you, being a part-time temporary employee, were chosen to cover it. It has nothing to do with valuing an employee, it has everything to do with the fact that, as a new hire with limited experience, they are fitting you in where you have value to them. Value isn't automatic. I'd ask about it, but, don't get all trash canny on them and talk about your being a valued employee, you are not anywhere near that description yet. At this point they don't know if you are or if they are just throwing money away training you. And for heavens sake, do not, tell them that it is because it messes up your sleep schedule. At that point, your value will hit rock bottom. It is easy to lose sight of the fact that they are paying you to do what they need to have done, not the other way around. You can choose to find another place to work, but, I think, you will find that the over all attitude of employers is the same. In the words of Don Corleone... it's business, it's not personal.