First, communicate with the teachers and ask for updates on grades and behavior. You may also ask for a parent-teacher conference to discuss your child's progress and needs. Ask that the school counselor be present to facilitate the meeting if you wish. Many schools provide email and other modes of communication, such as on-line progress reports.
Many times the administrator is the first person called to find out how a particular student is doing in class. The first contact should be with the teacher. My recommendation is to call the school secretary to find out when each of your child's teacher has a conference period. This is the time they should be able to discuss any questions you might have about how your child is doing in their class. I would also recommend having various methods of getting in touch with you (cell phone, work phone, home phone, email). This is very important that if you are at work during a particular teacher's conference period, they still have a way of getting information to you regarding your child. I would suggest speaking to the administrator only if you have made numerous attempts to speak to your child's teacher and they do not respond to these attempts.