The Early Developer Bias

The Early Developer Bias

Sport, especially at the elite/professional end of the spectrum tends to favour physically well-developed athlete’s. Several studies have in fact found that 80-90% of professional athletes were discovered and considered purely for having a birthday in the early part of the year. (more on this later in the blog). Contact team sports such as rugby, football and American football have been heavily criticised for this type of favouritism.



Rarely do athletes break into elite professional sports nowadays without having played and trained at their chosen sport for a significant period of time prior to reaching the top end. I am sure we can all think of examples of children or young adults who are seen as potential future sports stars well before they reach the end goal of professional sport. Now think back to that particular child you may have coached or trained alongside. What were the defining qualities he or she had that made you stand up and take notice? Was it to do with the way they moved, ran, jumped, evaded or just simply their sheer physical presence on the field/court. I bet one if not more of these traits is what drew you to take notice of this particular budding athlete. Don’t worry you are not the only person who this has happened to and unfortunately you will not be the last.  We have all had that experience of watching a young athlete, for example, a 14-year-old who is so physically imposing that he or she looks more like 18 years old. Coaches, parents and other players subconsciously are immediately drawn to this child as a physical specimen who if they have on their team is a huge advantage and if on the opposing side is going to cause all sorts of problems. This is what is termed in some circles as the 'early developer bias’s'.


The early developer bias is inherent favouritism towards children and young adults who have biologically matured earlier than their counterparts of the same chronological age. There is a lot of data and research currently being conducted in this area to better understand what advantages and disadvantages there are to being an early developer. Position statements have been put out by governing bodies like the RFU, RFL and the FA, in which all of them agree that selection bias based on physical stature is wrong and a more holistic approach should be utilised. However, this rarely happens. At grassroots and professional academy levels the system of scouting in most cases are heavily weighed in favour of the early maturing athlete. Often the size, strength, speed and power advantage will take them a long way in the selection process at earlier ages. The picture below is one that has been doing the rounds over the last few years. In all honesty, there is no article or data set that could display the discrepancies between early developers and the rest better than this picture. This is a picture of a very well known English rugby star (Billy Vunipola) sitting with his teammates. All of them played for the under 11 team when this picture was taken. Imagine been another under 11's team and coming up against a kid of this size? It is incredibly easy to see why the early developer bias exists. If you have a child who is naturally gifted with this sort of physical presence then as a coach you would do all you can to utilise and harness that to the advantage of your team would you not? The picture also does a great job of displaying something called the relative age effect (RAE).


The relative age effect (RAE) is a simple enough concept to grasp, RAE refers to the overall difference in age between individuals within each age group, which may result in significant differences in performance.


Billy Vunipola


Quartile 1 (Q1)– Athletes born in September–November
Quartile 2 (Q2)– December–February
Quartile 3 (Q3)– March-May
Quartile 4 (Q4)– June–August


The above quartile split is how children in the UK are grouped within the RAE scheme. In theory, a child born in either Q1 or Q2 should have a significant biological development advantage over children born in Q3 or Q4.  So much so that a study developed by Cobley and colleagues (2009) demonstrated that for every 2 elite athlete’s born in Q4 there were 3 more elite athletes born in Q1. The bias, especially at elite academy levels, heavily leans towards athletes born in the earlier quartiles were they may be identified as talented. This can be due to these athlete’s experiencing earlier maturation, especially in male athletes. The increase in physical attributes, in turn, may lead to players been selected more often which in turn due to increased exposure to the competition will mean greater access to resources and opportunities to excel. All of these factors drive deeper bias’s towards time, money and resources being dedicated to early maturing athlete’s.


On a side note, RAE doesn’t just work the one way. A child born in later quartiles of the year can in some cases be the early developer and the child born in early quartiles be the late developer. It is heavily dependant on parental height & weight and other factors such as socioeconomics, which all seems rather obvious but often overlooked.


There are clearly negatives to favouring early maturing athletes and some of them are listed below:


  • The early maturing athlete can rely too much on size and strength and neglect skill and technique.

  • Others will catch up and often the early maturing athlete will be left behind due to lack of technical, tactical and skill knowledge and practice.

  • Psychology and seeming lack of a challenge can impact enjoyment.

  • Can be dangerous for on time or late maturing athletes in some cases to come up against an early maturing athlete (refer back to picture).

  • Neglect of later quartile athlete’s means they may drop out sooner and not be given the same opportunities.


One of the hottest topics in youth sports development is bio banding. Bio banding is the practice of matching youth athlete’s in competition and training not dependant on their chronological age but on their level of biological maturity. Based on a few calculations a coach or practitioner can predict an athlete’s future adult height and weight. This can be then displayed as a percentage and athlete’s can then be grouped according to the percentage of future adult height. There are a number of advantages and disadvantages to using bio banding:



  • Gives early maturing athletes a challenge and means they have to rely on skill, understanding of the game and technical/tactical knowledge to succeed.

  • On-time and late maturing athletes get an opportunity to shine without fear of been dominated by the early maturing athlete.

  • Can mix players of different chronological age groups dependant on the percentage of adult height. This facilitates a different challenge for all athletes.

  • Coaches and scouts can potentially be evaluating athletes in a fair environment not simply losing potential ‘talent’ in the fog of early developer bias.



  • Bio banding should not be thought of as a straight swap for the normal chronological age groupings which still has its own advantages and disadvantages.

  • Heavily dependent on having access to large groups of athletes’.

  • Some early maturing athletes may not like the dent to their ego’s as they are no longer the most physically dominant athlete.

  • Psychologically speaking although a player may be a physical early maturer they may simply not be ready to go up against older children in training or competition.

  • Some later maturing athletes can become fantastic problem solvers when regularly training and competing against early maturing athlete’s.


Bio banding in principle is a great idea and there are many more merits than the ones listed above. But like anything in youth development a one size fits all methodology simply does not work in the long term. And that is what every coach needs to focus upon long term development. Bio banding can potentially solve the immediate issues but we are not aware of a study that looks at the long term effects of bio banding.


Early maturing athletes are a blessed population in sport and this blog is not meant to put a negative spin on them. If coached properly and nurtured like any other youth athlete then they can flourish and thrive in any environment. But do not neglect later maturing athlete’s in pursuit of in what is often short term successes. Youth sport and development should always be looked at in the long term. That child you may have called skinny or too small could actually be the hidden gem that you have been looking for. And in reverse, that child that you spend all your time heaping praise upon and selecting due to physical attributes may not be around for much longer. Don’t have tunnel vision develop each athlete equally and give them what they need and also the time to develop and flourish.


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