Laterality in handgrip strength was assessed by analyzing dynamometric data of the right and left hand in three samples of Lithuanian boys and girls aged 7–20 years. In addition, the influence of general physical training on the laterality of handgrip strength was explored in a sample of conscripts. A negative secular trend in handgrip strength of schoolchildren has been detected since 1965, and with increasing age, right-handedness has become more pronounced. Children that were ambidextrous (by grip strength) showed negative deviations in physical status more often than their right- or left-handed peers. During one year of physical training, the conscripts had a larger increase in grip strength of the left than in the right hand, and a marked shift in handgrip laterality toward left-handed and ambidextrous individuals was observed. The different impact of schooling and physical training on handgrip strength laterality might partly explain variations in the prevalence of handedness in different societies with divergent cultures and lifestyles (e.g., more or less sedentary).