An adult child could still be entitled to ongoing support if s/he is still considered a ‘child of the marriage’ as defined by the Divorce Act…
The ‘other cause’, more often than not, is post-secondary education. If an adult child is attending post-secondary studies, full time, this child will most likely be deemed “a child of the marriage” and therefore entitled to some degree of support.
It is important to distinguish between Guideline table support and Section 7 expenses. Guideline table support is the contribution made by the non-primary parent to the primary parent towards basis day-to-day expenses: for example, food, clothing, a roof over the child’s head. The amount is dictated by the non-primary parent’s income, generally without regard to the primary parent’s income Section 7 expenses—called Section 7 expenses because they are addressed in Section of the Child Support Guidelines—are above and beyond the table amount. Examples of Section 7 expenses would be daycare, medical and dental expenses not covered by insurance or a plan, possibly both expenses related to the child’s education and extracurricular activities. These expenses are shared by the parents proportionate to income.
Post-secondary education expenses are considered as a Section 7 expense; however, the sharing of this expense is different. The child is usually expected to contribute as well towards this expense, through grants, savings, income generated from part-time or summer employment, loans etc. There is no hard and fast rule as to how much the child should contribute towards the cost of post-secondary education. Generally speaking, the better off the parents financially, the less expected from the child.
In short, if the adult child resides at home and goes to his/her home university on a full time basis (part-time doesn’t cut it), the non-primary parent could be on the hook for both Guideline table support--at least for those months during which the child attends studies—and, as well, on the hook for a contribution towards the cost of these studies.
So, child support does not necessarily end when a child reaches 18. But surely, once a child has obtained his or her first post-secondary degree, diploma, certificate, that is it, that is all, right?
No longer. The reality of our generation is that many undergraduate degrees will not guarantee much more than a job flipping burgers at McDonalds. Often, further education is required to genuinely become self-sufficient. The Courts, as reflected in recent decisions, appear to acknowledge this fact. Whether or not a parent should contribution to further post-secondary expenses, depends on many factors, including but not limited to a) the parent’s financial circumstances, and b) the parents expectations for the child. For example, if the child’s parents are both doctors (or God forbid, lawyers), and the expectation was that ‘Junior’ was to follow in his or her parents’ footsteps, there is a good chance that a Court would require the parents to contribute towards the cost of the further post-secondary education.
 Shared parenting arrangements are usually handled differently, and I address this topic elsewhere.