In California, child support is calculated by using a statewide software called the California Statewide Uniform Child Support Guidelines. Child support uses each parent’s net income and the non-custodial parent’s timeshare with the child/children, which is one of the three components of child support.
Normally the court allocates school time to the custodial parent as the default mode unless the non-custodial parent requests otherwise. The court often views school time as the sole purview of the custodial time because the custodial picks up/drops off the child/children and is the sole parent on the school emergency notification.
The argument for having the timeshare not be 100% allocated to the custodial parent can be made by providing the Court information that the non-custodial parent is available and, in fact, provides care for the child when the child is sick or otherwise missing school. In fairness, if your child/children attend public school and you pay taxes, then you are paying for the school your child/children attend and their school time.
School time is not the sole purview of the custodial parent if the non-custodial participates in the pickup and drop off of the child/children i.e., pick up and drop off is done by both parents. Often both parents are listed on the school emergency notification.
Furthermore, the emergency notification roster is of less concern with the advent of cell phones. A lot of parents keep track of their children and for emergencies give young teenagers cell phones.
If you are the non-custodial parent, you should request all school time be either split 50-50 or at a minimum allocated per the custodial timeshare outside of school time. A 50-50 split would give the non-custodial parent an additional 9% timeshare during the school year.