I cannot find an open access link to the the Greek Schoolchildren study. It showed that boys at 6 had advantage over girls. This is a paragraph from a peer reviewed review of those studies:
"In early childhood, prior to puberty, sporting participation prioritises team play and the development of fundamental motor and social skills, and is sometimes mixed sex. Athletic performance differences between males and females prior to puberty are often considered inconsequential or relatively small . Nonetheless, pre-puberty performance differences are not unequivocally negligible, and could be mediated, to some extent, by genetic factors and/or activation of the hypothalamic–pituitary–gonadal axis during the neonatal period, sometimes referred to as “minipuberty”. For example, some 6500 genes are differentially expressed between males and females with an estimated 3000 sex-specific differences in skeletal muscle likely to influence composition and function beyond the effects of androgenisation while increased testosterone during minipuberty in males aged 1–6 months may be correlated with higher growth velocity and an “imprinting effect” on BMI and bodyweight . An extensive review of fitness data from over 85,000 Australian children aged 9–17 years old showed that, compared with 9-year-old females, 9-year-old males were faster over short sprints (9.8%) and 1 mile (16.6%), could jump 9.5% further from a standing start (a test of explosive power), could complete 33% more push-ups in 30 s and had 13.8% stronger grip . Male advantage of a similar magnitude was detected in a study of Greek children, where, compared with 6-year-old females, 6-year-old males completed 16.6% more shuttle runs in a given time and could jump 9.7% further from a standing position. In terms of aerobic capacity, 6- to 7-year-old males have been shown to have a higher absolute and relative (to body mass) VO2max than 6- to 7-year-old females . Nonetheless, while some biological sex differences, probably genetic in origin, are measurable and affect performance pre-puberty, we consider the effect of androgenizing puberty more influential on performance, and have focused our analysis on musculoskeletal differences hereafter."
This is the link to the study that looked at the two children's sports studies.
https://link.springer.com/article/10.1007/s40279-020-01389-3
Again, why would a school treat girls in a way that will not encourage them to compete and to do further sport?
Fair enough that it seems many parents on this thread disregard girl's needs to be able to compete fairly, or simply will ignore the studies that disprove their opinions that 'up to x age it is fair'. But the schools should not be treating girls this way.