At Patriot High School in Prince William County, the countdown is on.

“21 Days Remaining — Just Keep Swimming,” is scrawled on the whiteboard of a staff room at the sprawling new school west of Manassas. “Dewey Beach, Toes in the sand!” declares another in the science lounge. “July 18th: Fenway!”

These are the days, amid the crush of final exams, final projects and final straws, that a teacher’s addled thoughts turn to those most hallowed words of the scholastic calendar: June, July and August.

“This is our craziest time of year,” said Patriot science teacher Sarah Cureton last week as her students sweated over their annual Standards of Learning test. “You hear a lot about summer plans from teachers right now.”

But for many teachers, the vaunted “summer off” is a shrinking season. Although all the teachers interviewed at Patriot had some kind of getaway planned, they were booking around work-related obligations, such as workshops and second jobs, that fill in whole blocks in their planners.

“People always say, ‘Wow, you get the whole summer,’ ” said Theresa Carson, who teaches business at the school. “But there are literally just three weeks when I don’t have something to do related to school.”

The economic downturn and frozen salaries have put financial pressures on thousands of teachers across the country. In Prince William, where teachers earned an average of $59,367 in 2011, pay has barely budged in three years. That leaves the season as a time to teach summer school for extra pay or to find a job outside of school. Many teachers, aware that adding degrees to their résumé is one of the few ways they can boost their pay, fill the break with graduate courses.

And all educators have more to do each summer. They plan lessons, update materials and attend staff workshops, such as the mandatory statistics review Patriot math teachers took last summer to prepare for a new curriculum.

Teachers unions have long complained that the extra obligations haven’t come with extra pay.

“The notion of having the summer off was always more myth than reality,” said Randi Weingarten, president of the American Federation of Teachers. “Now the reality is that most teachers spend the summer either working a second or third job or working to hone their craft, usually on their own dime.”

For Delores Lucas, a Patriot English teacher, summer is more about business than the beach. After a June visit to Myrtle Beach, S.C., she will have about five days for her favorite summer idyll: fishing in the pond on her family farm.

Otherwise, she will be (deep breath) taking a graduate class at George Washington University, driving to an Advanced Placement literature institute in Richmond, attending a leadership academy in Manassas and a Standards of Learning workshop in Leesburg, presenting at two new-teacher orientations and joining her colleagues at a Franklin Covey Leader in Me session in August.

“I wouldn’t trade anything for the summer,” Lucas said. “But by the time I come back for the first day of school, I feel like I need a vacation.”

Still, the summer break remains one of teaching’s most-valued perks. After nine months of feverish focus on other people’s kids, June, July, August are Ctrl-Alt-Delete — a chance for an annual reboot.

“This is the only profession where you get to restart every year,” said Michael Bishop, Patriot’s principal. “Okay, maybe professional athletes, but we don’t get paid like they do. I’ve been encouraging my folks to take real time off. We’ve had a great year, and they need to resharpen their saws.”

Bishop said he encourages his teachers to make the most of the summer and worries about those who don’t get enough rest and relaxation.

“You can absolutely tell on the first day of school who has had a good summer and who hasn’t,” he said. “There’s a different way they carry themselves. When you’re relaxed, you can deal with the pressure.”

At Patriot, employees’ summer plans include at least two teacher weddings and one expected baby, a long-deferred foot surgery, a 700-mile bike ride and trips to local beaches, Thai rain forests and Peruvian ruins.

Like much in education, many of the teachers’ summer plans mix personal interests and professional duties. Two days after school ends, biology teacher Bryan Conrad will lead a study trip to Costa Rica. He and another teacher will be responsible for the morning routines of 19 teenagers — getting them out the door, sometimes before dawn.

“I told them to leave the curling irons at home,” said Conrad, who led a similar trip last year. “Believe it or not, I come back from this feeling rejuvenated. Physically exhausted, but mentally rejuvenated. You’re dealing with the students in a completely different manner.”

Like a third of teachers nationally, many Patriot faculty members will find seasonal work at jobs ranging from home remodeling to selling running shoes.

Cureton, the science teacher, will tend bar at a Manassas Applebee’s, a repeat gig that has helped her pay for her two master’s degrees. Special-education teacher Tammy Cabell-Pennix supplements her teacher pay with more teaching. Her summer means summer school.

For Cureton, the need to ensure some serious downtime reached a peak one recent morning as the end-of-the-year rush neared Tylenol proportions, and she got an urge to book a flight to the Dominican Republic.

“It was just one of those days when my classes were a bit overwhelming, and I could just see myself sitting on the beach,” she said.

Within hours, she had two e-tickets to Puerto Plata in hand.