A small acceleration in the rate of growth in height several years prior to the onset of the adolescent growth spurt, usually between 6.5 and 8.5 years of age. Findings for the First Zurich Longitudinal Study show a small, but significant mid-growth spurt in most height and length measurements, as well as pertaining to girth and width (e.g., chest circumference, bi-humeral and bi-iliac width). The spurt appeared to be slightly more pronounced in boys compared to girls. Given that it is quite a small spurt, there need to be statistical techniques capable of detecting it.
See Adolescent growth spurt, Developmental acceleration, Growth, Longitudinal studies