Too busy, bored or confused. These are just some of the reasons a spouse may not be interested in learning about his or her family’s financial plan. All understandable—and all potentially very costly.

Ellen Kamp knows this firsthand. She often worked 12-hour days as a corporate trainer on Wall Street and was the primary breadwinner for her family. Her husband, Eric, who worked from home as a freelance photographer, managed the household and the couple’s investments.

“Eric and I called it ‘division of labor,’ ” she says.

Mr. Kamp handled all of the interactions with their broker. Then he died unexpectedly, in 2006, and Ms. Kamp had to start managing the couple’s account and working directly with the adviser. “I had to learn about investing at the worst possible time,” she says. Making matters worse, she didn’t like the adviser. She eventually found a new one, learned more about personal finance and co-founded a group, the W Connection, that helps widows rebuild their lives.

Today Ms. Kamp urges spouses to take a more active role in their investments—and make sure they’re comfortable with all of the family’s advisers. If they’re not, she says, they should switch and know that they won’t be betraying the legacy of their late spouses.

While men or women may need to learn more about investing, studies conducted by financial-service companies have found that despite women’s gains in education and pay, many wives are still abdicating financial decisions to their husbands. According to a recent UBS report, 56% of married women still leave investment decisions to their husbands. Among millennial women, which the study identified as born between 1980 and 1996, some 61% of those who are married leave these decisions to their husbands. This lack of investment know-how is especially problematic as women are controlling more wealth and are likely to divorce or outlive their husbands.

What follows are some approaches advisers and spouses have used to get the less-interested partners more interested in, and skilled at, managing their investments and other finances.

LESSON PLAN

Sometimes the spouse who tends to manage the finances will try to teach the less-engaged spouse. This works sometimes—but the knowledgeable spouse has to tread carefully.

Ann Minnium, a financial planner in Scotch Plains, N.J., says one of her clients created a lesson plan for his previously uninspired wife. The husband made an outline of topics to cover, then created four lessons which would take an hour each to complete. Lessons included the basics of investments, insurance and wills.

After each lesson, they went out to dinner—without the children—to a restaurant of her choosing. The approach worked. While the wife has said she is happy to let her husband continue to manage the couple’s finances for as long as he is able, she is ready to step in if something were to happen to him, Ms. Minnium says.

Ms. Minnium says she also knows of a wife who holds quarterly money dates with her husband at his favorite restaurant. Before dinner, she leads the couple in a review of their investment accounts and encourages her husband to ask questions, no matter how basic.

DON’T GET FRUSTRATED

In cases where just one spouse handles the finances, and knows the subject well, it can be frustrating when the other spouse resists getting involved or has a hard time grasping it. And that frustration can backfire. The worst way to get an uninterested spouse involved is to force them to attend meetings with financial advisers and then ask things like: “Do you understand what he/she just said?” says Rocklin Senavinin, a financial planner in Little Rock, Ark. Such comments, while said out of frustration, can sound condescending.

In addition, phrases such as, “You have to learn this, you will be managing all of this on your own one day,” can overwhelm someone who doesn’t have any experience with investments, he says.

Instead, Mr. Senavinin says, it’s best to start slow and not expect the other person to learn everything at once. For instance, start with the basics such as stocks and bonds before explaining sector diversification or standard deviation.

MAKE IT PERSONAL

It can help to make the experience fun and relatable. For example, for a 50th wedding anniversary gift, Mr. Senavinin says, a husband asked the financial planner to teach his wife about investing. Mr. Senavinin says his company used the label “50th Wedding Anniversary Account” for the wife’s account. And by following energy stocks (their son worked in the energy industry) she quickly became interested in learning more.

“Now, she’s more engaged than her husband,” Mr. Senavinin says.

Some advisers try to inspire uninterested spouses by talking about their retirement dreams. Financial planner Ariadne Horstman knows a couple where the husband wasn’t interested in learning about the family’s investments. However, he loved to imagine himself retiring early or traveling the world.

To get him engaged on her financial-planning software, the Palo Alto, Calif., planner would show the husband various scenarios that depicted how much more the couple would need to invest or save to achieve his dream. Seeing the scenarios projected on large computer screens got him interested in investing, Ms. Horstman says. She was able to gradually teach him about various investment vehicles such as stocks and exchange-traded funds.

“Most people get interested and excited when talking about what they want and how to go about getting it,” Ms. Horstman says.

ALLOW TIME

Simply making sure financial advisers send materials such as a couple’s financial statements a day before client meetings can help boost an uninvolved spouses’ engagement, says Carol Schleif, deputy chief investment officer at Abbot Downing, an asset manager and financial-planning firm based in Minneapolis.

Doing so may give the spouse time to absorb the information beforehand so they can prepare and formulate questions. “They may be less likely to ask questions during the meeting if they feel put on the spot,” she says. Letting a less-active spouse schedule the meeting and take the lead in asking questions can also give them a greater sense of confidence, advisers say.