Navarro Patón, RubénPueyo Villa, SilviaMartín Ayala, Juan LuisMartí González, MariacarlaMecías Calvo, Marcos2021-06-042021-06-042021Int. J. Environ. Res. Public Health 2021, 18(11), 5514; https://doi.org/10.3390/ijerph18115514http://hdl.handle.net/10347/26384The purpose of this study was to determine the probability that preschool children have severe motor difficulties or are at risk of motor difficulties, according to quarter of birth and gender. Five hundred and eighty-eight preschool-age children were evaluated, of which 318 (54.08%) were boys and 270 (45.92%) were girls, with a mean age of 4.66 years (SD = 0.53). The Movement Assessment Battery for Children-2 (MABC-2) was used to collect the data. The results obtained were the following: Regarding students with severe motor difficulties: 6.7% born in quarter 1 (Q1); 13.3% born in the second quarter (Q2); 20.0% born in the third quarter (Q3); and 60.0% born in the fourth quarter (Q4). The probabilities found (OR) were: Q1 vs. Q2 (OR = 3.15; p < 0.05); Q1 vs. Q3 (OR = 4.68; p < 0.005); Q1 vs. Q4 (OR = 12.40; p < 0.001); Q2 vs. Q4 (OR = 4.04; p < 0.001); and Q3 vs. Q4 (OR = 2.65; p < 0.005). The adjusted ORs, with respect to the probabilities of having severe motor difficulties, were the following: Being born in Q4 is 13.03 times more likely than being born in Q1 (p < 0.001); those born in Q3 are 4.85 times more likely than those born in Q1 (p < 0.05); and those born in Q2 4.14 times more than those born in Q1 (p < 0.05). The conclusion is that children born in Q4 are more likely to be classified as children with severe difficulties compared to children born in the other quarters of the same yeareng© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)Atribución 4.0 Internacionalhttp://creativecommons.org/licenses/by/4.0/Relative age effectChildhoodMABC-2Motor competencejournal article10.3390/ijerph181155141660-4601open access