It really depends on who's doing the reference check, who's providing the reference, and the type of job the candidate is trying to land.

In some companies reference checks are done by the HR department and are just a basic verification of role, length of employment, salary, and reason for separation.

Also, some companies have a policy of only allowing a manager to disclose basic information when providing a reference for a former employee, even if the manager would like to say good things about the former employee's performance.

But, unless restricted by company policy, a good manager will personally do reference checks before hiring a candidate and will try to find out as much as possible about the candidate during the checks. The more professional the job, the more thorough the reference check is likely to be. If there are issues from a previous job, it's often best to deal with them during the interview process before the reference checks happen.

When I do a reference check, I like to ask this question: "If, in the future, you were in a position to offer this person a job, would you hire him/her?" Pretty frequently, a former manager who's been saying vaguely positive things about the candidate will end up saying "no", which leads to a deeper conversation that helps me figure out whether the candidate will fit well in my company.

length of employment & disciplinary actions

See State Laws on References and Statements By Former Employers (http://tinyurl.com/State-Laws-on-References)

I think their only allowed to ask basic work related questions like length of employment, job title, and attendance.