The Boston Consulting Group (BCG) is in the business of helping the world’s leading companies solve their most difficult problems. So when it came time to solve the problem of how to retain more female talent at the firm, BCG didn’t just reach for an off-the-shelf program. It consulted itself and did extensive internal research that unlocked a breakthrough idea.

BCG found that the gender gap was not completely explained by more traditional workplace concerns such as work-life balance, maternity leave, unequal pay, or differential ambitions. Through its analysis, BCG unearthed a new and different explanation: for women at the firm, the apprenticeship experience (a critical component of the consulting model, where junior team members learn alongside seasoned partners) was as important, if not more important, than just about any measure of work-life balance. As a result, in 2010 BCG launched Apprenticeship in Action (AiA). This program was designed around the core belief that improving women’s apprenticeship experiences would improve and accelerate their careers at BCG. In combination with other programs—such as increased focus on recruiting diverse talent, tailor made development processes, individualized sponsorship, and enhanced flexibility and predictability at work—AiA has proven to be an astounding success.

Eight years into AiA’s implementation, the number of women in BCG’s US consulting ranks has more than doubled. To date, BCG’s executive committee consists of more than 35% women, and promotion rates among women in the United States have risen across all cohorts, with a 22% increase among senior managers. The attrition rate of senior women has slowed by 5%, and, perhaps most tellingly, retention of mid-career women is now on par with that of their male peers. And due to its effectiveness and the universality of its founding principles, AiA has also resonated with other diverse groups and men.

BCG’s CEO Rich Lesser says AiA has been transformational for the firm’s commitment to diversity:

Diversity honestly is our lifeblood. We’ve found that diverse teams get to better answers, build deeper collaboration with clients, and are more likely to understand all the elements required to enable long-term success in a rapidly changing world. And if we can’t make it work for everyone then we’re not behaving as responsibly as we should, but we’re also just missing opportunities to build BCG to its full potential.

BCG’s internal research clearly showed what opportunities were missing for the women at the firm. Women wanted more mentorship, connection, and coaching. And for good reason—mentorship and sponsorship can be career-makers, particularly for women. For example, one Catalyst study found that men with mentors earned 6% higher salaries than men without, while women with mentors earned 27% higher salaries than women without them.

To solve for this complex need, BCG partnered with leadership development consultancy BRANDspeak to develop AiA around three core components of apprenticeship: relational connectedness, strengths-based development, and coaching for a range of effective communication styles.

In the past, employees widely reported relationships as being overly “transactional.” So with an eye on boosting connections, AiA helped managers better understand the significance of mentorships and equipped them with easily accessible methods to help cultivate those relationships. One recommended tactic: use travel time to schedule touch points. Something as simple as a ten-minute phone call can make all the difference to a junior colleague in need of guidance.

According to Jessica Rabie, a Project Leader who joined BCG in 2016, this practical approach has been extremely effective:

I have been inspired again and again by a great leader who has been there to help me when I was struggling. After a hard week working through difficult problems or client relationships, having someone to offer support, give guidance, and remind you what you’re great at, is invaluable.

The move toward strengths-based development was also welcomed by women and men alike—63% of staff previously felt feedback focused too heavily on areas for development. In contrast, AiA helped managers frame personal development feedback through an individual’s strengths, allowing them to leverage skills—rather than deficiencies—to accelerate improvement. This has transformed the way advisors coach, and the way advisees respond to challenges. Namely, with more self-awareness and confidence. Says Rabie:

Strengths-based development has made me more aware of what my unique strengths are and how I can leverage them in situations that are more challenging for me. For example, to use my ability to task-manage to build in time to reflect on the analysis portion of my work…helping me push toward insights that are more impactful to my client. I’ve also learned to leverage my ability to build strong relationships to see problems from my client’s perspective, which helps ensure our messaging resonates.

Prior to AiA, BCG largely operated under “male” communication norms (described as direct or even aggressive) but the firm soon recognized that the most effective communicators do not have a one-size-fits-all style. Rather, they can access a range of styles and tailor their approaches to each audience. With AiA, BCG has pioneered training that focuses on areas like “building rapport” and “reading the room,” as well as individualized coaching that helps people identify and strengthen their own communications gaps.

AiA is having a resoundingly positive impact. Satisfaction with BCG’s efforts to retain women has increased by 20% for all women at the firm, and by 30% among its senior women. And for the seventh consecutive year, BCG has been ranked in the top five of Fortune’s “100 Best Companies to Work For.”

While AiA was born out of the apprenticeship needs of women, the program has helped reshape the culture and mindset of the firm as a whole. Says Lesser:

AiA is accelerating change at BCG because it’s improving our culture and creating a better working environment for everyone. Its key to success has been coaching others to recognize and reward the benefits of diverse styles, instead of coaching those with diverse styles to fit into the existing culture.

For other leaders seeking similar change within their organizations, Lesser offers some practical advice. In short, it takes significant effort to accelerate gender inclusion but we must treat it like the business imperative it is:

First, treat this like any other business priority. Otherwise it’ll never get the focus and energy it deserves. Second, you must get men involved. It cannot just be that women are supposed to help other women succeed. Third, don’t just implement best practices. Tailor what you do specific to your business situation. Lastly, you have to measure the change you intend to make. And you have to have goals that you’re really committed to, that you’re willing to talk publicly about. You’re willing to stand up and say, “We’re not as good as we should be, but here’s what we’re trying to do.” That’s how real change happens.

Because of BCG’s own commitment to making lasting change, what began as a program to benefit women has grown into a better way of working for an entire organization. It has also created a consulting firm better equipped to help its clients implement their own gender and diversity improvement efforts. So the success of AiA could soon become a model for even more positive change in other companies.