Back-to-school shopping? Do your tax homework.

The list of back-to-school supplies can be daunting — and costly — from a new pair of sneakers to binders and lunch boxes. Retailers estimate that Americans will pay more than $870 per student to return their kids to K-12 schools this fall when they add all the clothing, electronics, shoes and other needed items. That’s no small price tag, so shoppers need to do their homework and not just look for good value (and keep to a reasonable budget) but also factor in timing.