I have had the most success using a leveling system for K-2.  This takes the form of a clip chart.  Each student has a laundry clip with their assigned number on it (for the sake of anonymity) and the clip moves up or down to reflect the day's behavior.  Everyone starts every day on green, the middle color, that represents Ready to Learn.  Staying on green or going above is wonderful!  There are consequences for each color below green, culminating in contacting the parent/guardian.  

The collaboration between parent and teacher is so important to every child's success, and this provides the best form of easy communication about behavior for the parent and in a way the child clearly understands.  This system is very private, as the chart is tucked away and clipping up or down can be a private discussion depending on the situation.  Your child will always know why their clip is moving as close to when it happens as possible.  

Your child will record their color for the day in their folder so you can see at a glance their behavior for the day!  If your child clipped down to a lower color at any point, I will always record what rule was broken so that you can discuss it with your child, too.  If the behavior is a more severe transgression or if your child is a star student (outstanding behavior and attitude!), you can expect a call from me just to keep you in the loop!