Elizabeth Barrow celebrated her 100th birthday at a backyard gathering with her son and three grandchildren in the coastal Massachusetts town where she raised her family and cooked lunches in a school cafeteria.

A month later, in September 2009, Barrow was found dead at a local nursing home, strangled and suffocated, with a plastic shopping bag over her head. The killer, police said, was her 97-year-old roommate.

Workers at the nursing home, Brandon Woods in South Dartmouth, had months earlier described the roommate in patient files as being “at risk to harm herself or others.’’

The roommate — despite her age and dementia — was charged with murder. The authorities did not focus on the nursing home, though. Brandon Woods claims that, except for some minor arguments, the two women got along nicely. When the roommate was deemed unfit to stand trial and committed to a state hospital, the case essentially disappeared.

Barrow’s only son, Scott, is still trying to hold the nursing home accountable. “The woman had a history of problems,’’ Scott Barrow said of the roommate this month. “She should not have been living in that room with my mother.’’

Scott Barrow was barred from taking Brandon Woods to court in 2010 because his mother’s contract with the nursing home contained a clause that forced any dispute, even one over wrongful death, into private arbitration.

He has been trying ever since to get back to court, and next month he will finally get that chance. A Massachusetts state court is scheduled to hear his case against the home, which has evolved into much more than a lawsuit about one woman’s death. It has become a test of a legal strategy to prevent nursing homes across the country from requiring their residents to go to arbitration, where there is no judge or jury and the proceedings are hidden from public scrutiny.

Arbitration clauses have proliferated over the past 10 years as companies have added them to tens of millions of contracts for things as diverse as cellphone service, credit cards, and student loans. Nursing homes in particular have embraced the clauses, which are often buried in complex contracts that are difficult to navigate, especially for elderly people with dwindling mental acuity, or their relatives, who can be emotionally vulnerable when admitting a parent to a home.

State regulators are concerned because the secretive nature of arbitration can obscure patterns of wrongdoing. Recently, officials in 16 states and the District of Columbia urged the federal government to deny Medicaid and Medicare money to nursing homes that use the clauses. Between 2010 and 2014, hundreds of cases of elder abuse, neglect, and wrongful death ended up in arbitration, according to an examination by The New York Times of 25,000 arbitration records and interviews with arbitrators, judges, and plaintiffs.

Judges have consistently upheld the clauses, The Times found, regardless of whether the people signing them understood what they were forfeiting. Once a contract is signed, judges have ruled, it is legally binding.

Scott Barrow’s case is pivotal because, with the help of his lawyers, he has overcome an arbitration clause by using the fundamentals of contract law.

As is often the case when elderly people are admitted to nursing homes, Scott Barrow signed the paperwork containing the arbitration clause on his mother’s behalf.

Although his mother had designated Barrow as her health care proxy — someone authorized to make decisions about her medical treatment — his lawyers argued that he did not have the authority to bind his mother to arbitration. In 2014, a judge ruled in his favor.

It is a straightforward argument that is catching on. Appeals courts across the country have tossed out arbitration agreements signed by family members of nursing home residents.

For years, judges hearing elder-abuse cases rejected arguments that arbitration clauses in nursing home contracts were unfair because they were signed by people who did not understand them or perhaps even realize they existed.

In a circuit court case involving a man in a Mississippi nursing home who could not read, write, or sign his name, the judges held that under state law, “illiteracy alone is not a sufficient basis for the invalidation of an arbitration agreement.’’

“Any normal human being would say that these contracts don’t pass the smell test. But the courts don’t accept this,’’ said Martin S. Kardon, a plaintiff’s lawyer in Philadelphia with a focus on nursing home cases.

A few years ago, Kardon and a small network of lawyers across the country tried a different tack. They began making hypertechnical arguments about the validity of nursing home contracts.

They argued that unless family members had power of attorney, they lacked the authority to agree to arbitration.

“We had to start speaking the language of judges,’’ Kardon said.

When Scott Barrow, now 67, brought his parents to the nursing home in 2006, signing the paperwork seemed like little more than a formality, the final step of an already tough process.

At first, his parents — sweethearts since they met working at a textile mill — shared the same room at the home, a tidy brick building with a decorative pond outside. After his father died the next year, his mother had a string of roommates. Known for walking the halls, asking other residents if they needed hugs, Elizabeth Barrow made friends easily.

Things changed in 2008 when she got a new roommate, Laura Lundquist, who was moved because of an argument with her previous roommate, Scott Barrow’s lawyers said in a court filing.

The change of scenery did not seem to help Lundquist, who had been diagnosed with dementia, delusions, anxiety disorder, depression, and paranoia.

On Aug. 21, Elizabeth Barrow turned 100. A month later, back at the nursing home, a simple disagreement between the roommates escalated.

It began when Barrow asked a nursing assistant to move a table from the foot of Lundquist’s bed so she could get to the bathroom. At that request, Lundquist got out of bed, screamed, “was verbally abusive and hit’’ the nursing assistant, records show. It took two staff members to calm Lundquist.

Officials at Brandon Woods and its lawyers did not respond to requests for comment.

In the court papers, lawyers for the nursing home said Elizabeth Barrow had assured the nurse that she felt safe in the room “and that Ms. Lundquist would cool off.’’

At 6:20 the next morning, staff found Barrow in bed with a plastic bag on her head and the covers pulled up. The table was back at the foot of Lundquist’s bed.

“I can’t do anything for my mother,’’ Barrow said, “but I want people to realize that they have to investigate nursing homes. Everyone could end up there.’’