In this article, Oklahoma State University’s Jentre Olsen reviews research on the effects of instructional time.
Historically, Oklahoma’ public schools operated on a standard 180-day school calendar. However, nearly every district in the state has gradually adopted hourly calendars over the past 10-15 years, which is permitted under Oklahoma state law. Even though this legal framework offers local flexibility, it has led to schools choosing to offer the minimum number of days (166 days) by packing minimum hourly requirements (1,086 hours) into fewer school days during the year. What’s more, state law allows approximately five professional development days and two parent-teacher conference days to count as instructional days. As a result, Oklahoma’s students effectively attend school for an average of 159 days each year.
In recent years, the legislature has sought to address the state’s short school calendar. In the 2025 legislative session, virtual days, often considered equivalent to a day off, were restricted to two days per year. This law will go into force next school year. As of this writing, the legislature has also passed a new law raising the minimum number of instructional days to 173 from 166 days, thereby adding seven days to school calendars.
To understand how raising the number of student days may influence outcomes in Oklahoma, this article synthesizes national and international research. In short, the overall body of research suggests that increasing instructional days is a meaningful academic reform. Evidence further indicates that concentrating more instructional hours into fewer school days is likely to be detrimental for students. At the same time, it is critical to note that the extent of the positive effects derived from more school days may be amplified by concurrent strategies that support instructional quality and capacity.
Research on Instructional Time
Expanded instructional time can increase students’ exposure to content, help students consolidate previous learning, and strengthen intervention and enrichment opportunities. A substantial body of research indicates that increased instructional time is, on average, associated with improved student achievement. In a recent meta-analysis from 2024, researchers synthesized 74 causal studies, finding that greater instructional time was related to positive gains in student achievement. Research also offers suggestive evidence indicating that increasing hours in each school day as a way of reducing the total number of days in the year may have negative academic consequences for students.
Moreover, researchers have shown that increasing instructional days supports student learning, but the extent of the impact of more days depends on how such time is used. That is, the effects of instructional time vary across school contexts and depend on the instructional conditions. Studies also demonstrate that expanded time produces the largest academic gains when implemented as part of broader school improvement efforts.
In other words, extending the school year expands schools’ capacity to support learning, while instructional quality determines how effectively that added capacity is used. One of the key takeaways from research then is not whether additional days matter, but how they are integrated with professional learning, intervention systems, and coherent instructional practice.
US-based and International Research
In the United States, research on instructional time has historically been connected to broader school improvement efforts rather than treated as an isolated input. Early scholarship emphasized engaged learning time and opportunities to learn as vital organizational features of successful schools, alongside coordinated instructional practices and strong instructional leadership. Subsequent time-on-task research has similarly demonstrated that the amount of time students spend actively engaged in learning activities influences achievement, but only when instructional activities are purposeful and well structured. Together, this body of previous scholarship has established a consistent premise: more instructional time amplifies learning when embedded within effective instructional systems.
Contemporary research reaches similar conclusions. A comprehensive systematic review by Patall and colleagues (2010) found that extending the school day or year is associated with modest academic gains on average, with larger effects occurring when additional time is used strategically for targeted instruction rather than uniformly added to existing schedules. More recent analyses reinforce this interpretation. Kraft and Novicoff (2024) reported that instructional time operates through multiple dimensions, including scheduling structure, instructional coherence, and student engagement, indicating that additional time enhances the effectiveness of existing instructional practices rather than substituting for them.
Adding to this idea, McMullen and Rouse (2012) found that mandatory year-round calendar conversions produced uneven academic effects, suggesting that changes to instructional time are likely to interact with local implementation capacity. Collectively, the US-based literature shows that expanding instructional time increases learning but does not independently guarantee large improvements.
While US-based research highlights how instructional time operates within U.S. systems, international research provides additional insight by distinguishing between access to learning time and the effectiveness of its use. Cross-national analyses have routinely demonstrated that greater instructional time is associated with improved academic outcomes, with the strongest effects observed in systems where baseline exposure to schooling is limited.
International studies further highlight implementation constraints. Expanding instructional time without corresponding investments in staffing capacity can contribute to teacher fatigue and reduced instructional effectiveness. These findings reinforce a consistent conclusion across contexts: instructional time expands learning opportunity, while instructional quality determines the extent of gains from added time.
Variation in Instructional Time
A common benchmark is a 180-day school year in the United States. However, across the US, states regulate instructional time in different ways, typically through a mix of minimum day requirements, hourly requirements, or hybrid models. Because districts in some states may satisfy requirements through total hours rather than days, some schools compress instructional time into longer daily schedules. What this means, in practice, is that over the course of a K–12 education, students in states using hourly school calendars often lose the equivalent of a year to one-and-a-half fewer years of schooling compared to state systems operating near standard 180-day calendars.
Table 1 illustrates variation in instructional days across selected high-performing education systems, highlighting differences in students’ total exposure to school time and how Oklahoma provides substantially fewer instructional days than many other school systems.
It is also important to note that studies show diminishing marginal returns once students receive sufficient instructional exposure, indicating that additional time alone does not uniformly produce achievement gains. Large-scale international comparisons similarly emphasize the idea that it is how instructional time is implemented. Synthesizing evidence across multiple countries, the OECD (2021) found that extended instructional time yielded the greatest benefits when used for targeted remediation, individualized support, and structured learning opportunities rather than simply lengthening existing schedules. In other words, systems that combine adequate time with instructional coherence experience larger academic improvements than systems that increase time without accompanying changes to instructional practice.
The Downsides of Compressing More Time into Fewer Days
When instructional time is concentrated into fewer school days, students experience longer gaps between learning opportunities. Research indicates that cognitive fatigue increases later in extended school days, reducing the effectiveness of instructional minutes late in the day. By contrast, systems that distribute the same number of instructional hours across more days provide richer opportunities for engagement, reinforcement, and intervention. As a result, these systems generally produce better academic outcomes than those concentrating hours in longer daily blocks. A meta-analytic review by Cooper et al. (1996) documented achievement declines across summer breaks, demonstrating that learning may depend on sustained exposure rather than isolated instructional periods. More days in the school year thus increases opportunities to practice skills, revisit content, and receive academic and social support.
More Instructional Days: Teachers’ Workload and Fiscal Implications
Expanding instructional days can improve learning, but doing so may place new demands on systems, educators, and resources. In particular, instructional time policies also redistribute demands on educators. In compressed calendar models, fewer school days necessitate longer daily schedules and faster instructional pacing, possibly increasing fatigue for both students and teachers. Research on instructional time highlights workforce sustainability not only as a function of total days worked, but of how instructional time is structured across the year. That is, extending the number of days may increase teachers’ contractual obligations, but compressing time into fewer days may concentrate workload intensity for teachers.
Adding days carries fiscal consequences, including recurring costs related to salaries, transportation, utilities, and support services. Recent legislative proposals make these tradeoffs explicit. House Bill 3151 requires school districts operating on an hours-based calendar to increase the minimum number of instructional days from 166 to 173 beginning in the 2027–28 school year, effectively adding seven instructional days, while maintaining the state’s 1,086-hour requirement.
This bill is tied to new state investment, with approximately $175 million in additional funding proposed to support the transition, effectively allocating resources at a per-day rate to offset the costs of extending the school year. These provisions underscore that expanding instructional time is fundamentally a resource allocation decision, not simply a scheduling change.
Implications for Oklahoma
The central policy question is not whether time matters, but under what conditions will additional days translate into the greatest possible improvements. Research demonstrates that the impact of additional days is largest in school systems where students already receive comparatively limited instructional time. In Oklahoma, students receive substantially fewer instructional days than national norms, meaning that school calendar expansion addresses reduced access to instruction rather than extending already sufficient time.
At the same time, added days alone may not generate drastic improvement. The overall research evidence presented in this article suggests that the extent of the impact of additional instructional days depends on three conditions: how time is used instructionally, the capacity of the educator workforce, and the fiscal capacity of districts to support calendar changes. Without alignment across these conditions, public investment in additional days may not reach its full potential.
When used coherently within instructional programs, additional days can improve our state’s academic performance. The benefits of additional days emerge when schools use them for targeted intervention, reteaching, and enrichment. School calendar changes that outpace workforce capacity or district resources can reduce instructional quality. Compensation structures, planning time, and staffing supports should function as implementation mechanisms rather than ancillary considerations.
Oklahoma’s schools almost certainly need more student days in the calendar year. However, as Oklahoma continues to consider instructional time policy, the issue is not only how many days students should attend, but also how the school year is designed to support teaching and learning. Ultimately, school calendar policy should be treated as part of a broader school improvement strategy rather than an isolated reform if it is to have its greatest effect on student outcomes.
Author Bio
Jentre Olsen is the Brock Chair of Innovative Educational Leadership at Oklahoma State University.
