WASHINGTON — Hundreds of thousands of children in Northern Virginia head back to school Tuesday, including roughly 186,000 in Fairfax County, the 10th-largest school system in the nation.

“Our teachers and our administrators have been working real hard over the summer making that sure we are ready,” said Jeff Platenberg, the school system’s assistant superintendent for facilities and transportation services. “We’re looking forward to a really successful year for our students.”

Kids in Alexandria, Falls Church, Fredericksburg and the counties of Arlington, Stafford and Spotsylvania will also head back to class.

School officials in all systems are urging drivers to watch for students who may be walking to school or who may be at bus stops.

Fairfax County alone has more than 1,600 buses — more than Greyhound, and the biggest school-bus fleet in the country — carryong more than 137,000 students, and that “really puts a lot of volume out there that otherwise might not be on the road,” said Platenberg.  “Although it’s an exciting time, we ask for our community’s patience.”

Last year, Fairfax County police say, 147 tickets were given out for passing stopped school buses.

If a school bus is stopped, with its stop sign out and red lights flashing, drivers in both directions must come to a stop unless they are separated from the bus by a median.

“A lot of people don’t seem to remember that, but that really is the law,” Platenberg said.

Virginia’s schools, and schools in Maryland’s Eastern Shore county of Worcester, are the last to go back.

A number of Maryland school systems, including Montgomery and Prince George’s counties, started school Aug. 29.

Many Virginia schools systems don’t start classes until after Labor Day because of the  so-called Kings Dominion law that passed in 1986. It requires schools to start after Labor Day, unless they get a waiver for an earlier start. The intent is to boost the region’s tourism industry, and give students who work a chance to work through the traditional end of summer.

Maryland Gov. Larry Hogan last week mandated that schools begin after Labor Day, in part for a similar reason — to help the state’s tourism industry.

The order, which goes into effect next year, will require schools to end their school year by June 15, but won’t change the overall number of instructional days.