January 28, 2026 • Updated February 6, 2026 • 28 min read

Age for School: Kindergarten Entry Ages and Cutoff Dates by State

When should your child start kindergarten? The answer depends on where you live, when your child was born, and a growing body of research about how age at school entry affects academic and social outcomes. This guide provides kindergarten entry cutoff dates for all 50 states, explores the science behind the "relative age effect," examines the debate over academic redshirting, and compares school starting ages around the world. Whether you are wondering about your child's chronological age or planning ahead for important age milestones, this comprehensive resource will help you make an informed decision.

Kindergarten Entry Age Cutoffs by State

In the United States, there is no federal law establishing a nationwide kindergarten entry age. Each state sets its own cutoff date -- the date by which a child must turn 5 to be eligible for kindergarten in that school year. The table below shows the cutoff date for every state and Washington, D.C. For detailed information about legal ages for other milestones like driving and voting, see our comprehensive guide.

Note that some states allow districts to set their own cutoff dates within a range, and some offer transitional kindergarten (TK) programs for children who narrowly miss the cutoff. Always confirm the exact cutoff with your local school district, as policies can change. The Education Commission of the States maintains an updated database of these policies.

The most common cutoff date is September 1, used by roughly 20 states. This aligns with the typical school year start in late August or early September. States with later cutoffs (New York's December 1, Connecticut's January 1) mean that some kindergartners may still be 4 years old when they start school, while states with earlier cutoffs (West Virginia's July 1, Hawaii's July 31) ensure most students are 5 or nearly 5 at entry.

Use our age calculator to determine your child's exact age on any given date and see whether they will meet your state's cutoff. You can also check their age in days for precise calculations.

History of Kindergarten Age Requirements

The concept of kindergarten -- literally "children's garden" in German -- was invented by Friedrich Froebel in 1837 in Germany. Froebel believed that young children learned best through play and hands-on activities, a revolutionary concept at the time. The first kindergarten in the United States opened in Watertown, Wisconsin in 1856, established by German immigrant Margarethe Schurz.

Evolution of Age Requirements in America

Early American kindergartens typically enrolled children ages 4-6, with no standardized age requirements. The push for uniform cutoff dates began in the early 20th century as kindergarten became more widespread:

• 1900-1920: Most states that offered public kindergarten set no specific age cutoff. Enrollment was at parental discretion.
• 1920-1950: States began establishing cutoff dates, typically ranging from September 1 to December 31. The age of 5 became the standard entry age.
• 1950-1980: The September 1 cutoff emerged as the most common choice, aligning with the school year calendar. According to the U.S. Census Bureau, kindergarten enrollment grew from 12% of 5-year-olds in 1940 to 80% by 1980.
• 1980-2000: Many states began moving cutoff dates earlier (from December/October to September/August), partly in response to research on the relative age effect and rising academic expectations.
• 2000-Present: California notably moved its cutoff from December 2 to September 1 between 2012-2014, introducing transitional kindergarten (TK) for children who missed the new cutoff.

The Academic Expectations Shift

A major driver of changing kindergarten cutoffs has been the dramatic shift in academic expectations. As Education Week and other education researchers have documented:

This "kindergarten is the new first grade" phenomenon has fueled both the trend toward earlier cutoff dates and the rise of academic redshirting, as parents worry their children are not ready for increasingly rigorous expectations.

The Relative Age Effect

The relative age effect (RAE) refers to the well-documented phenomenon that children who are among the oldest in their school grade tend to outperform younger classmates in both academics and athletics. This effect was famously explored by Malcolm Gladwell in his 2008 book Outliers, where he noted that an outsized percentage of elite Canadian hockey players were born in January, February, and March -- the months immediately after the January 1 age cutoff for youth leagues. Understanding the age difference between the oldest and youngest students in a class is crucial for grasping this phenomenon.

How the Relative Age Effect Works

In a typical kindergarten class with a September 1 cutoff, the oldest children (born in September) may be nearly a full year older than the youngest children (born in August). At age 5, a 12-month age gap represents a 20% difference in time alive and a significant difference in cognitive, physical, and emotional development. Older children tend to:

• Score higher on reading readiness tests and early math assessments
• Exhibit greater emotional regulation and social skills
• Be taller and stronger, giving them advantages in youth sports
• Be less likely to be held back a grade
• Be less likely to be diagnosed with ADHD or other learning difficulties

The Data: Birth Month and Academic Achievement

Research from the National Bureau of Economic Research has quantified the relative age effect across multiple studies:

The effect is strongest in early grades and diminishes over time, but never fully disappears. As documented by researchers at NIH, even in high school, students who were the youngest in their class are slightly less likely to enroll in advanced courses or take AP exams.

ADHD Misdiagnosis and Birth Month

One of the most concerning findings related to the relative age effect involves ADHD diagnosis. Multiple large-scale studies have found that the youngest children in a class are significantly more likely to be diagnosed with ADHD than the oldest.

The Harvard Study

A landmark 2018 study published in the New England Journal of Medicine analyzed 407,846 children and found that in states with a September 1 kindergarten cutoff, children born in August (the youngest in their class) were 34% more likely to receive an ADHD diagnosis than children born in September (the oldest). Crucially, this pattern did not exist in states with different cutoff dates -- the elevated diagnosis rate always fell on the youngest students relative to the cutoff, not on children born in a particular month overall.

ADHD Diagnosis Rates by Birth Month (September Cutoff States)

Why Does This Happen?

Researchers believe this is because the normal immaturity of younger children is being misinterpreted as a clinical condition when compared to their older, more developmentally advanced classmates. A 5-year-old compared to a 6-year-old will naturally:

• Have a shorter attention span
• Be more physically restless
• Show less impulse control
• Have more difficulty following multi-step instructions

These are all symptoms of ADHD, but they are also normal characteristics of being younger. The CDC recommends that clinicians consider a child's age relative to their classmates when evaluating for ADHD, but this recommendation is not always followed in practice.

Implications for Parents

If your child is among the youngest in their class and a teacher or physician suggests an ADHD evaluation, consider:

• Requesting that the evaluator account for relative age in their assessment
• Seeking a second opinion from a specialist familiar with the relative age research
• Asking whether the behaviors could be age-appropriate rather than pathological
• Considering whether the child might benefit from waiting a year before starting school (redshirting)

Academic Redshirting: Pros and Cons

Academic redshirting is the practice of delaying a child's entry into kindergarten by one year, so they start at age 6 instead of 5. The term is borrowed from college athletics, where "redshirting" means keeping a player out of competition for a year to extend their eligibility. Redshirting is most common among parents of boys with summer birthdays (June, July, August) who are concerned about their child being the youngest in the class. This relates directly to birthday calculations and school planning.

How Common Is Redshirting?

Approximately 4-9% of US kindergartners are redshirted each year, according to data from the National Center for Education Statistics. The practice is more common among:

• Boys (roughly twice as common as girls)
• White families and families with higher socioeconomic status
• Children with summer birthdays close to the cutoff date
• Families in states with earlier cutoff dates
• Families in competitive school districts

Redshirting Rates by Demographics

Arguments for Redshirting

• Developmental readiness: An additional year of maturation can make a meaningful difference in a 5-year-old's cognitive, social, and emotional development. Children who start kindergarten at 6 may be better prepared to handle the academic and social demands of school.
• Avoiding the relative age disadvantage: By holding a child back, parents ensure their child is among the oldest rather than the youngest in their class, potentially gaining all the advantages associated with being older.
• Sports advantages: An extra year of physical development can translate to meaningful advantages in youth athletics, which may lead to more playing time, better coaching, and greater confidence.
• Long-term academic outcomes: Some research suggests that older kindergarten entrants earn slightly higher standardized test scores throughout elementary school.
• Reduced ADHD misdiagnosis risk: Being older in the class significantly reduces the likelihood of ADHD misdiagnosis, as documented above.

Arguments Against Redshirting

• Short-lived academic gains: Multiple studies, including a 2017 Stanford study, found that while redshirted children initially outperform younger peers, the gap narrows significantly by third grade and may disappear entirely by middle school.
• Social and emotional concerns: A child who is significantly older than classmates may struggle socially, particularly in adolescence when developmental differences become more pronounced. Being the first to go through puberty, or being a year older than peers when discussing age-appropriate topics, can create awkwardness.
• Opportunity cost: An extra year before kindergarten means an extra year of childcare costs and a year less of earning potential at the other end of the child's career.
• Equity concerns: Redshirting disproportionately benefits affluent families who can afford an extra year of preschool or childcare. This can widen the achievement gap between socioeconomic groups, as lower-income children enter at the minimum age while wealthier peers delay.
• Grade-level effects: When many parents in a community redshirt, the average age of kindergartners increases, which can inadvertently raise the difficulty level of the curriculum and put non-redshirted children at an even greater disadvantage.

Long-Term Outcomes: What the Research Shows

School Starting Ages Around the World

School starting ages vary dramatically across countries, reflecting different philosophies about early childhood education. Some nations believe formal academics should begin early, while others prioritize extended play-based learning before transitioning to structured education. For context on how different countries approach age-based regulations generally, see our legal ages guide.

The Finnish Paradox

One of the most striking findings in international education is that countries with later school starting ages (Finland, Estonia, Sweden) consistently rank among the top performers on international assessments like PISA, while countries with very early school starts (England, Northern Ireland) do not outperform them. Finland, which does not begin formal academic instruction until age 7 and emphasizes play-based learning in early childhood, is frequently cited as evidence that starting school later does not harm academic outcomes and may even help by allowing children more time to develop foundational social and emotional skills through play.

According to the OECD PISA assessments, Finnish 15-year-olds consistently score in the top 10 globally despite starting formal education 2-3 years later than many peers. This suggests that age at school entry is far less important than the quality of education once it begins.

School Starting Age vs. PISA Reading Scores (2022)

When to Start Kindergarten: A Decision Guide

Deciding when to enroll your child in kindergarten is one of the most consequential early education decisions parents face. Here are the key factors to consider:

Consider Your Child's Individual Readiness

Rather than focusing solely on their chronological age, assess your child across multiple dimensions:

• Academic skills: Can they recognize some letters and numbers? Can they hold a pencil and attempt to write their name? Do they show interest in books and being read to?
• Social-emotional readiness: Can they separate from you without extreme distress? Can they share, take turns, and follow simple rules? Can they express their needs verbally?
• Physical development: Can they use scissors, buttons, and zippers? Can they sit still for 10-15 minutes? Are they toilet-trained?
• Attention and focus: Can they listen to a story for 5-10 minutes? Can they follow two-step directions?

The Readiness Checklist

Talk to Preschool Teachers

Your child's preschool teachers have observed them in a classroom setting and can provide valuable insight into their readiness. They can compare your child's development to that of their peers and identify specific areas of strength or concern.

Consider the Cutoff Date Context

A child born one week before the cutoff faces a different situation than one born three months before. If your child's birthday falls within a few weeks of the cutoff, the decision is much closer and deserves more careful consideration. If their birthday is several months before the cutoff, they will likely be in the middle of the age range for their class, reducing concerns about being too young. Use our birth year calculator to understand your child's position relative to peers.

Avoid Comparisons to Older Children

When visiting kindergarten classrooms to assess readiness, remember that the children you see have already had months of kindergarten experience. Your 4- or 5-year-old should not be expected to match the skills of children who have been in school for several months.

Consider Long-Term Implications

A child who is redshirted will be the oldest in their class all the way through school. They will turn 18 before many of their classmates, turn 21 in college a year early relative to their class, and enter the workforce a year later than if they had started on time. For more perspective on age milestones throughout life, see our detailed guide. Think about whether these timeline shifts matter to your family.

Famous People Who Started School Late (or Early)

Looking at successful people who were among the oldest or youngest in their classes can provide perspective -- though individual outcomes vary dramatically regardless of school entry age.

Famous "Late Starters" (Redshirted or Held Back)

Famous "Early Starters" (Young for Their Class)

The takeaway: school entry age matters statistically at the population level, but individual factors like motivation, support, and opportunity matter far more for any specific child's success.

School Age Charts and Visualizations

This chart shows how kindergarten cutoff dates are distributed across the United States, from the earliest (July 1) to the latest (January 1).

Age Range in a Typical Kindergarten Class

This visualization shows the age spread in a kindergarten class with a September 1 cutoff, on the first day of school:

The oldest student may be nearly a full year older than the youngest, representing ~20% more life experience at this age.

Global School Starting Age Comparison

Frequently Asked Questions

Calculate Your Child's Exact Age

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