Training & Development

Early developers in swimming: is your daughter behind?

Early developers in swimming often look ahead because growth arrived sooner, so your daughter isn't necessarily behind. Birth-month effects tend to fade. Compare her times with her own.

September 21, 2026 · 3 min read

Idea in Brief

  • One birth year holds many growth stages. Body size at twelve cannot diagnose talent.
  • Birth-month effects fade with age. Portuguese swimming research finds the clearest pattern in younger groups.
  • Compare her with herself. A personal best removes other swimmers’ growth timing from the measure.

Behind the blocks, the tallest swimmer stands a head above the shortest. The heat sheet puts both in the same escalão, or age category. For 2026/27, each Infantis and Juvenis escalão holds one birth year. That doesn’t put their bodies at the same growth stage. A study measured the same children each year from 8 to 18. Among girls not active in sport, peak growth speed averaged 11.9 years, with a range from about 9.5 to 14.5. For boys, it averaged 13.6 years, with a range from about 11.3 to 16.2. These group figures aren’t a timetable for any child.

That spread can look like talent when selection begins. A review of maturation in youth athletes says selection and exclusion often follow maturity, mainly during puberty and the growth spurt. Talent develops while bodies and behaviour change in highly individual ways. A systematic review of relative age in swimming found the effect in 58.65% of participants across the included studies. It was strongest in younger groups, fell with age, and inverted in older groups. It was about twice as strong in boys as girls. These patterns can’t explain one child’s result.

Birth month adds another layer in Portugal. A study of the best 50 Portuguese swimmers in each main individual event, aged 12 to 18, covered 7,813 event participations. Birth dates were uneven across almost all age groups and both genders. More swimmers, especially boys, were born in the first two quarters of the year. The effect appeared among 12-year-old girls and boys aged 12 to 15. Within that top 50, birth quarter mostly made no difference to performance.

The FPN’s long-term model gives a similar warning. It says early-maturing swimmers often succeed sooner due to maturity, rather than better swimming skills. Late-maturing swimmers may be given harder training just to keep up. The model links this response to early specialisation and shorter careers. It also says some early maturers leave when later developers beat them. The FPN reports only a low link between formative results, especially in Infantis, and senior results.

Nothing here calls for a change to training. The coach handles that. You can change the comparison you make out loud. Your swimmer’s personal best doesn’t depend on who else is bigger or born earlier. If you’re asking whether a time is good for her age, compare it in context. If her times have stalled, the plateau year is a separate question. An escalão sorts entries. It doesn’t sort bodies by maturity. If growth itself worries your family, ask your doctor.

Share it with your swimmer

Keep the result in its proper frame:

  • Under 12 (you’re driving). “Let’s compare this swim with your last one.” One clear measure is enough.
  • 12–15 (sharing the wheel). “One birth year can hold many growth stages.” This names the gap without labelling anyone.
  • 16+ (they’re driving). “Your time tells us more than the size of today’s field.” This keeps the comparison on their swimming.

Stay aligned with your coach

The coach decides training and reads progress in the pool. You choose which comparisons are made at home. Ask, “What signs of progress are you watching besides place?”

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