Checking job or employment references is time-consuming and frequently unsatisfactory, as many employers, despite recent legislation, refuse to offer more than dates of employment, salary history and job title. Secondly, if you're not careful, each reference check can turn into a friendly chat during which you don't obtain the information you need to make an objective decision about hiring your candidate.
As with most Human Resources processes, a standard reference checking format is useful. You can easily compare candidates and ensure you are asking the "right" questions to make an educated decision before offering the applicant a job with your company.
I don't check references until we are ready to make an offer to a candidate. This saves staff time and demonstrates our respect for the candidate. After all, you don't know whether his current employer or her favorite professor even know That he or she is looking for a new position. (I prefer candidates who tell their employer, but realize this isn't always possible, or even desirable.)
Here is the format I use to check references.