What is the test to vary child support under section 17 of the Divorce Act?

Section 17 of the Divorce Act requires proof of a material change in circumstances before the court can vary child support provisions of a corollary relief order. An application to vary is not an appeal of an originating order, nor is it an opportunity to retry a prior proceeding. The existing order must be treated as correct as of the date the order issued. A material change is one which has not been foreseen, or could not have been reasonably contemplated by the judge who made the original order: Gordon v. Goertz 1996 CanLII 191 (SCC), [1996] 2 SCR 27. A material change must be more than a temporary or minor change; the change must be a substantial, continuing one.