Under Section 510(a), a child support order may only be modified based on two specific conditions:

1. Substantial Change in Circumstances:  

A parent can request a modification of child support if they can show a "substantial change in circumstances" since the original order was entered or last modified. A substantial change may include significant shifts in the financial status of either parent or the child’s needs. This could be due to a change in employment, a significant increase or decrease in income, or changes in the child’s needs, such as healthcare or educational expenses. Importantly, events that were foreseeable at the time of the original order, unless specifically mentioned, are generally not considered a substantial change. The court may also specify in its original order or a subsequent agreement which future events would or would not constitute a substantial change, preventing unnecessary litigation over anticipated changes.

Prospective Changes Only: Modifications to child support are generally prospective, meaning that they only apply to payments due after the motion to modify has been filed and proper notice has been given to the other parent. Support payments that are already past due are generally not retroactively modified.

Under Section 510(d), child support obligations generally terminate upon the emancipation of the child. This typically occurs when the child reaches the age of 18. However, if the child is still attending high school, child support continues until the child either graduates from high school or turns 19, whichever occurs first. It is important to note that child support does not automatically terminate upon the death of a parent. If a parent obligated to pay support dies, the child support order may still be enforced or modified, and the court can require the support obligation to be paid from the deceased parent's estate as equity may require.

Section 510(f) clarifies that filing a petition to modify or terminate child support does not delay enforcement proceedings. This means that while a modification request is pending, the existing support order remains in effect, and the court may continue to enforce it through measures such as wage garnishment, non-wage garnishment, or restraining orders to ensure compliance with the support order.

Even after the death of a parent, the right to petition for educational expenses or ongoing child support continues under Section 510(e). The court may award sums for the child’s support or educational needs out of the deceased parent's estate, and the time for filing such claims is governed by the Illinois Probate Act. This provision ensures that a child's right to financial support is protected even in the event of the supporting parent’s death.