IF you had to incur some significant cost (e.g. you paid for the class yourself, and it was expensive) or some other significant detriment (such as to take the class, you gave up a previously-scheduled vacation; you switched from day to night shift to accomodate the class; etc.) then you may be able to enforce the promise of a raise under the theory of "promissory estoppel." However, without some significant detriment to you to take the class--which detriment the employer either had to be aware of when they asked you to take the class, or at least reasonably should have been aware of--you cannot enforce the promise  under this theory; and if cannot enforce it under promissory estoppel, then you most likely cannot enforce it at all, since employers are generally free to set, change, or refuse to change employee compensation at will. Also, to enforce the promise against an unwilling employer, you'd have to sue your employer, which has its own costs.