It has been reported that young age of school onset has important effects on academic and behavioral outcomes. Although there are studies using multinational data, data from low and middle income countries are few. As part of a larger study about mathematics learning difficulties, the aim of the present study was to evaluate the age of school entry on mathematics ability and general ability in standard tests and emotional and behavioral problems reported by their teachers among 2058 third grade students in Ankara, second biggest and capital city of Turkey. Results indicated lower mathematics and general abilities and higher hyperactivity/impulsivity, inattention and emotional problems scores as well as less prosocial behavior in the youngest group of children. Effect sizes were largest for general ability and mathematics ability. Our data were largely consistent with previous studies from other countries, and extended the literature by providing data from a middle income country.