Let's get one thing straight...you will not get promoted "if you work hard enough". Promotion is by competition, internally and externally, and Clerical Officer (CO) is the lowest entry clerical grade. I take it that yopu mean the college will let you continue your current course part-time? If so, take the job. If you don't need the job and wouldbe happier to finish your degree on the chance (no guarentees!) of getting a better-paid, more fulfilling job from it, then don't take it.
The real question, IMHO, is how high is the bar you want to set yourself in your career path?