In the ever-evolving education landscape, teachers need to be constant learners to keep up. However, since teacher professional development (PD) can vary significantly in design, implementation, and duration, little evidence links teacher PD and student achievement (see, for example, The Mirage). A recent working paper by Ariana Audisio, Rebecca Taylor-Perryman, Tim Tasker from Leading Educators, and Matthew P. Steinberg from George Mason University explores how some features of Leading Educators' program produced benefits for student learning.

In 2015, Leading Educators, a nonprofit organization that focuses on providing PD and leadership training, designed and offered a two-year fellowship program for teachers, principals, and district leaders in three regions across the U.S. The program started with leadership development sessions, classroom instruction coaching, and bias awareness and mitigation training. Then it focused on improving pedagogy and content knowledge in specific areas of ELA and math. Fellows were expected to take what they learned back to their schools to build a stronger instructional culture among their teacher colleagues. The fellowship program proved effective. Participating schools saw their students perform better in ELA and math compared to the schools' performance prior to the program. These effects were statistically significant under the following conditions:

• When fellows participated in the program for two years
• When the school had lower "saturation" (defined below)
• When staff from the district participated alongside school-based staff

The study found that a well-designed PD program should consider four factors to maximize its effectiveness and create a positive impact on teacher practice and student learning outcomes. Each of these factors was related to student outcomes, but not always in the way one might expect.

1. Saturation - Saturation, put simply, looks at the proportion of school staff and fellows participating in the program. Counterintuitively, schools saw greater positive effects at lower levels of saturation. In other words, student outcomes were better for schools where fewer fellows enrolled in the PD, which may also reflect that teams were often assigned to participate, rather than choosing to engage in the PD. The authors hypothesize that the negative results in schools with higher ratios of participating fellows could be due to individual fellows receiving more personalized coaching than the teams did. Likewise, fellows choosing to enroll individually may be more motivated than those assigned to participate by their principal in teams (related to enrollment type below), although saturation does not measure people's reasons for signing up.
2. Enrollment Type - Enrollment type differentiates between fellows who joined the program as individuals versus as a member of a school-based team. In both subjects, individuals had positive effects after just a year, but for teams, positive effects didn't show up until two years of PD in ELA, and there were no positive effects for teams in math. Coupled with saturation, a well-founded PD program should be tailored to address the specific challenges and opportunities that arise from different types of participation (team or individual) and in the different content areas. PD that recognizes and accommodates these differences can lead to more relevant and applicable teacher-learning experiences.
3. Duration - The duration of the Leading Educators' PD program was either one or two years, depending on the region. They found that longer PD allows for deeper engagement, sustained learning, and more opportunities for implementation and reflection. In fact, fellows enrolled for two years had significantly greater effects in ELA and math, compared to those schools enrolled for 15 months or less, which had no significant effects. The thinking is that longer-duration PD enables teachers to receive ongoing support and adapt their practices over time, while shorter PD can be effective for targeted content development, but might have a limited impact on significant shifts in teaching practices without follow-up and reinforcement.
4. Local Education Agencies (LEA) Participation - The participation of LEAs, or staff from school districts, in PD initiatives can considerably influence the program's success. The study showed that when staff in LEA-level roles participated alongside their school-based colleagues, schools saw a more positive effect on ELA and math compared to when only school-based fellows enrolled. When LEAs actively engage in PD planning and implementation, they can align the PD with their overall educational goals and ensure coherence with other district initiatives. LEAs also have the capacity to provide necessary resources, support, and time for teachers to participate effectively. When LEAs are committed to PD, it signals the importance of ongoing learning within the district.

In summary, these factors are interconnected and should be carefully considered when designing and implementing teacher professional development. Saturation and enrollment type affect the collective impact, duration influences the depth of learning, and LEA staff participation shapes overall support and sustainability.