The measurement problem
Is your athlete
getting better, or
just getting older?
A thirteen-year-old will get faster over six months doing nothing at all. Which means almost every before-and-after number you have ever been shown by a training facility is partly just growth.
What everyone else measures
Two dots and
a hopeful arrow.
The standard model in this industry is a one-time assessment: you come in, you get tested, you get a profile of strengths and weaknesses, and you get a plan. That is a genuinely useful thing and we do it too — it is the first session of every athlete we take.
But it answers where are you now. It does not answer the only question a parent is actually paying to have answered: did this work?
To answer that, you need a second measurement, a third, and a fourth — and you need something to compare them against besides the first one.
The two lines that matter
Separating the work
from the calendar.
Illustrative shape, not one athlete's data. Real figures live on the Results page.
We establish a growth baseline
At intake we estimate how far along your athlete is in their physical maturation — how much of their adult height they have already reached. It takes a height, a weight, and both parents' heights. No imaging, nothing invasive.
We re-test on a fixed cadence
Every two weeks on the qualities that move that fast, and a full re-test at the close of every 12-week block. Same gates, same protocol, same order, same time of day — because a trend line is only real if the measurement never changes.
We report the gap, not the raw gain
Your report shows the measured result, the gain expected from maturation alone, and the distance between them. That distance is what you bought. If it isn't there, you'll see that too.
The growth baseline
How we work out where
your athlete is in their growth.
Two fourteen-year-olds can be four years apart biologically. One has already been through his growth spurt; the other hasn't started. Training them the same way — or judging their test results against the same expectation — is the most common mistake in youth athletic development.
The method
Percentage of
adult height.
We estimate how much of their eventual adult height your athlete has already reached — their %PAH. The method comes from Khamis and Roche (Pediatrics, 1994), and it needs four things: a carefully taken standing height, body mass, their exact age, and the average of both biological parents' heights.
That's the whole intake. No imaging, no blood work, nothing invasive, and — unlike the older methods it replaced — no sitting-height measurement, which is the step most likely to be taken badly and quietly wreck the estimate.
Height is measured to a fixed standard, three times, and we take the median. A maturity estimate is only as good as the measurement underneath it.
The four stages we place athletes into
Pre-pubertal
The growth spurt hasn't begun. This is the window where coordination, movement skill and speed mechanics are learned most easily — and where loading is kept deliberately conservative.
Pubertal onset
The spurt is beginning. Programming stays in the pre-spurt pattern, but we start watching growth closely — because what comes next changes how the athlete should be trained.
Circum-PHV
Peak height velocity — the fastest-growing stretch, and the highest-risk, noisiest window in the whole process. Limbs lengthen faster than control adapts. Test scores get erratic. Loading rules change here.
Post-PHV
The spurt is essentially finished. The athlete can now tolerate and benefit from the heavier, more adult-shaped training that would have been a poor trade eighteen months earlier.
A rule we hold ourselves to
You will get a band, never a decimal. This estimate is good enough to place an athlete into one of four wide stages and to adjust how we read their numbers. It is not precise enough to justify a fine-grained individual maturity label, and we won't hand you one dressed up as a measurement. Any facility quoting your child's biological age to one decimal place is selling you precision that the underlying method does not have.
The instruments
Nothing here
is a stopwatch.
Four pieces of testing equipment, one report. Every number your athlete is measured on comes off the same gear, in the same order, every single time — which is the only reason a two-week trend line means anything.
Force production
Force plates
Measures how much force your athlete puts into the ground, how quickly they can produce it, and how evenly each leg contributes. Left-right asymmetries show up here long before they turn into an injury.
Speed
Dual-beam laser timing gates
Two beams per gate instead of one, so a swinging arm can't trip the clock early. Splits acceleration from top-end speed — because an athlete who starts well and fades needs the opposite of one who builds late.
Power
Jump pad
Contact time and flight time on every jump. That gives us jump height, reactive strength, and how efficiently your athlete stores and returns elastic energy — the quality that separates quick from merely strong.
Power at speed
Keiser pneumatic resistance
Measures power through the whole range of a movement, not just how much weight moved. Shows us where your athlete actually produces power and where it drops off — which decides how their programming gets built.
All four feed one growth-adjusted report — not four printouts you have to reconcile yourself.
The protocol
Why every re-test
looks identical.
A trend line is only real if the measurement never changes underneath it. So every testing session at GPS runs the same way: the same warm-up immediately beforehand, the same tests in the same order, the same equipment and setup, the same rest between attempts, and the same time-of-day window.
The order isn't arbitrary — speed first, then jumps and reactive strength, then maximum strength, then mobility. Least fatiguing to most. Conditioning never runs before power, because a tired athlete tests like a slower athlete and you would read that as a regression.
Sprints and jumps are scored best-of-three, reactive strength best-of-five. New athletes get a familiarisation exposure before anything is logged as a real number, because the first time you do a test you are learning the test, not showing us your ceiling.
If a test can't be run under standard conditions on a given day, we don't log it. A contaminated number is worse than a missing one — it looks like data, and it will sit in your athlete's trend line lying to both of us.
Why two weeks
Test twice, twelve weeks apart, and you have a line with two points — and a line with two points can be drawn through anything. A bad night's sleep at either end moves it. Re-testing every two weeks, six times across a block, means no single session decides the story. You see a direction, and you see it early enough to change the plan while the block is still running rather than finding out at the end.
Reading the report
What a percentile is,
and what a good one
actually looks like.
A raw number tells you almost nothing on its own. Is a 4.9-second 30-yard dash good? It depends entirely on who's running it. A percentile answers that: it places your athlete against others their own age. At the 60th percentile, they are faster than 60 out of 100 athletes in their age band.
This is the mechanism that makes growth visible. If your athlete's raw sprint time improves but their percentile stays flat, they got faster at exactly the rate their peers did — which is to say, they grew. If the percentile climbs, they passed the kids who were also getting older. That gap is the part training is responsible for.
It also explains something that confuses parents: an athlete can post a personal best and still lose ground. Getting better is not the same as getting better faster than the field, and only one of those is evidence that the training worked.
Where this comes from
We didn't
invent this.
Maturity-adjusted assessment is established practice in long-term athletic development research. Sports scientists have measured it this way for decades, and professional academies — particularly in European soccer — have used maturation status to interpret youth testing data for years.
What is unusual is doing it for a fourteen-year-old in Lake in the Hills, on a two-week cadence, and handing the parent a report that shows the gap in plain language.
Our claim is not that this science is ours. It is that we run it, on your athlete, and we put money behind the answer.
The honest boundaries
What this method
does not do.
Every measurement approach has limits. A program that won't tell you its limits is either not looking for them or not telling you.
It does not predict adult height
We estimate how far along the growth curve your athlete is today in order to read their numbers correctly. That is not a forecast of how tall they will end up, and we won't let it be used as one.
It is not a selection tool
A maturity band explains why a test result looks the way it does. It is not a verdict on an athlete's ceiling, and it should never be used to decide who is worth developing. Late developers are the athletes this most often protects.
It is an estimate, and we band it
The method places athletes into four wide stages. It is not precise to the decimal, so we don't report it that way — and we would be suspicious of anyone who does.
One re-test never decides anything
Sleep, illness, a heavy practice, exam week — all of it moves a number. Any single session can mislead. Only the direction across several re-tests is worth acting on, which is exactly why we test as often as we do.
Use this on us too
Five questions to ask
any facility — including this one.
Most advice for parents evaluating a training program stops at "make sure they measure something." That isn't enough. Measuring the wrong thing consistently still tells you nothing. These five questions separate a program that can prove its work from one that is asking you to take it on faith.
- 01
What exactly will you measure, and on what equipment?
"We'll track their progress" is not an answer. You want named tests on named instruments. A stopwatch has roughly a tenth-of-a-second human error in it — which is larger than the improvement a twelve-year-old will make in a month. If the measurement error is bigger than the effect, the number is decoration.
- 02
How often will you re-measure, and under what conditions?
Two tests twelve weeks apart give you a line with two points, and a line with two points can be drawn through anything. You want a cadence frequent enough to show a trend, run under standardised conditions — same equipment, same order, same time of day. A number collected differently is not comparable to the one before it.
- 03
What are you comparing the result to?
This is the question almost nobody asks, and it is the one that matters most. Compared only to their own starting number, every growing athlete improves. Compared to other athletes their own age, you learn whether they gained ground or merely kept pace. Ask which comparison you're being shown.
- 04
What happens if the numbers don't move?
A program confident in its measurement will tell you what it changes when the trend is flat — and what it costs you. A program that has never considered the question will reassure you instead. Notice which answer you get.
- 05
Can I see the raw numbers, not just a summary?
You are entitled to your athlete's actual data — the test values, the dates, the conditions. A summary with no underlying numbers cannot be checked, and anything that cannot be checked cannot be trusted.
We wrote these to be used on us. If GPS ever can't answer one of them for your athlete, that is a real problem and we'd want to hear about it.
Why we'd rather be measured
Measuring it this way
is how we can put money
behind it.
We measure your athlete against what growth alone would have delivered. If training doesn't beat growing up, you don't pay for that block. We can only make that promise because we measure the growth itself.
Guarantee terms are defined in the enrollment agreement · 90%+ attendance & tracking required
Straight answers
Questions parents
actually ask.
The five we get asked most about how any of this is actually measured.
01 What does growth-adjusted actually mean?
It means we compare your athlete's test results against what athletes at the same stage of physical maturity typically gain over the same window — not just against their own starting number. The gap between those two is the part training is responsible for.
02 Why isn't a before-and-after number enough?
Because a 13-year-old who does nothing at all will still get faster and stronger over six months. Any program can show a before-and-after improvement in a growing athlete and call it a result. Without a growth baseline, you cannot tell coaching from calendar.
03 How do you know what stage of maturity my athlete is at?
We estimate percentage of adult height reached, using the athlete’s current height and weight and an average of both biological parents’ heights. It is a standard, non-invasive method — no imaging, no blood work. We report it as a stage, not a number to compare against teammates.
04 How often do you re-test?
Every two weeks on the metrics that respond that fast, with a full re-test at the end of each 12-week block. That cadence is what makes the trend line real instead of two dots on a chart.
05 What if the numbers show training is not beating growth?
Then you do not pay for that block. That is written into the enrollment agreement, and it is the reason we measure this way rather than just claiming it.
06 What is a percentile, and what counts as a good gain?
A percentile places your athlete against others their own age — at the 60th percentile they are ahead of 60 out of 100 athletes in their age band. A few points inside one two-week window is noise. A sustained climb of 20 or more percentile points across a block is a genuine change in where your athlete sits among their peers, not a good day on the timing gates.
07 Can my athlete post a personal best and still have lost ground?
Yes, and this is the single most useful thing a growth baseline tells you. If the raw number improves but the percentile stays flat, your athlete got faster at exactly the rate their peers did — which is to say they grew. Getting better is not the same as getting better faster than the field, and only one of those is evidence the training worked.
08 Does the maturity estimate predict how tall my athlete will be?
No, and we will not let it be used that way. We estimate how far along the growth curve they are today so we can read their test numbers correctly. It is not a forecast of adult height, and it is not a selection tool — a maturity band explains why a result looks the way it does, never who is worth developing.
09 What happens if my athlete is a late developer?
They get read against where they actually are rather than against the calendar, which is the whole point. Late developers are the athletes most often written off in youth sport for testing behind peers who are simply further through their growth spurt. Placing them in the right stage protects them from that, and it changes how their training is loaded.
10 Do we get the raw numbers, or just a summary?
The raw numbers — the test values, the dates, and the conditions they were collected under. A summary with no underlying data cannot be checked, and anything that cannot be checked should not be trusted. That applies to us as much as to anyone else you might train with.