By June, many high school juniors are just plain tired of tests.

Those aiming for selective colleges are likely to have taken the PSAT in the fall and then the ACT or SAT (or both) multiple times, first in practice sessions, then for real. Many sat in May for Advanced Placement exams in subjects including chemistry, English and U.S. history. Some took rigorous International Baccalaureate tests. That’s not counting all the tests they took in class all year in quest of the best grades for college applications.

Then comes a chore that might catch them by surprise: SAT Subject Tests. These are perhaps the most obscure pieces of the college application puzzle, with rising debate among admissions professionals on whether they are even needed.

Claire Kaplan, 17, of Potomac, Md., a junior at Georgetown Visitation Preparatory School, said after taking the tests in math and U.S. history one recent Saturday that she was relieved to be done with her year of standardized testing but found the whole exercise frustrating. “It’s not really an accurate representation of someone’s knowledge,” she said, “but of how much you can pay to get tutored.”

The multiple-choice subject tests take an hour apiece, a third the length of the regular SAT. Each one focuses on a discrete subject such as math, biology (ecological or molecular) and even modern Hebrew. They are required by a few colleges, recommended by a few more and plummeting in usage nationwide.

About 220,000 high school graduates in the Class of 2017 took a subject test, according to the College Board, which oversees the exams. That total was down 30 percent compared with six years earlier. By comparison, more than 1.3 million in the Class of 2017 took at least one AP test, and millions took the SAT or rival ACT.

This year, Tufts University became the latest to drop its subject-test mandate, saying it found “very minimal correlation” between test scores and student performance in the first year of college. Worried that test-taking expenses would burden some families, Karen Richardson, the university’s dean of undergraduate admissions and enrollment management, said in an email “it became clear that eliminating the requirement was the right thing to do.”

Yet the subject tests remain a fixture in the admissions process for a certain set of students who want to keep their options open and are advised to take them by teachers in the know, experienced older siblings or, often, paid consultants.

On the first Saturday of this month, Luca Quadrani took subject tests in U.S. history and what is known as “level 2” math — tailored to students who have taken algebra, geometry and precalculus. The 16-year-old from Bethesda, Md., a junior at Walt Whitman High School, had already taken the regular SAT and AP tests in U.S. history and English language and composition.

“To balance between subject test studying and actual schoolwork, it’s been a little bit of a hassle, I’ll tell you that,” Quadrani said. “But I managed.”

The College Board said it is exploring how to reduce the testing burden and whether AP tests can play a larger role in admissions. Many colleges award course credit for high AP scores, and they encourage students to list those scores on applications. But typically, colleges do not explicitly require AP scores — in part, experts say, because the program is not available in all high schools. Subject tests, by contrast, are available nationwide.

The College Board says the subject tests enable students to stand out by showing mastery in a given area. “We share legitimate concerns about duplicative testing,” said Jane Dapkus, vice president of college readiness assessments for the nonprofit organization. “While the content of SAT Subject Tests and AP Exams are not identical, there is overlap in some of these exams.”

The subject tests trace their history to the beginning of the 20th century, when essay exams in various topics became known as the “college boards” and were given at the end of related college-preparatory courses.

Eventually, the tests switched to a multiple-choice format and became an achievement-oriented supplement to the main exam. The SAT itself, overhauled twice in the past 15 years, is now billed as an achievement test, too. Its maximum score is 1600 — 800 in math and 800 in reading and writing. The subject tests also yield scores of up to 800 apiece.

MIT is among the few schools requiring subject test scores. It asks applicants for one score in math and one in chemistry, biology or physics.

“We do find they’re helpful and predictive,” said Stuart Schmill, MIT’s dean of admissions and student financial services. Some students perform better on a math subject test than on the math section of the SAT or ACT, Schmill said. In such cases, he said, additional scores can “give us more confidence to admit those students.”

Schmill acknowledged that many applicants also take AP tests in calculus and various sciences. Unlike subject tests, those are designed to measure college-level work. But Schmill said students often take the AP tests in May of their senior year, too late for applications. He said that MIT publicizes the subject tests in marketing materials because many potential applicants are unaware of them.

“People will say, ‘What? Huh? What are those?’ ” he said.

Harvey Mudd College, also focused on science and engineering, requires one subject test in math and one in any other field a student chooses. Some major universities recommend that students with engineering ambitions send math and science scores.

Harvard, Yale and Princeton universities, and a few others, recommend sending two subject test scores. Georgetown University strongly recommends three.

James Murphy, director of national outreach for test-preparation company the Princeton Review, said recommending a test, instead of requiring it, is confusing and gives an unfair edge to well-off students with access to expert guidance. He said colleges should be “more transparent about the role [subject] tests play in their admissions process.”

Ben Campion, 16, of Silver Spring, Md., will be a junior in the fall at Gonzaga College High School. He took a subject test in molecular biology June 2. He said he hadn’t known about such tests until a few weeks ago and was “kind of shocked” to learn some colleges expect them.

“First foray into the SAT world,” Campion said after emerging from the testing center at Woodrow Wilson High School in Northwest Washington. He called the experience less stressful than an AP European history exam he had taken a few weeks earlier. He felt well prepared. But he added: “Standardized testing, in general, just isn’t fun.”