Malawi uses an 8-4-4 education system and the official entry to primary school is six years. However data from EMIS shows that the ages of new entrants to Standard One ranges from 4 years to 11 years. Standard One efficiency indicators for primary education show that the promotion rate is at 62.7%; repetition rate is at 24.5%; and dropout rate is at 12.8% (EMIS, 2010). These are the worst indicators in as far as the efficiency indicators of the primary system are concerned. In addition to this, health indicators show that 47% of the children are stunted, 13% are underweight and 4% are wasted (NSO, 2011, p. 133). Hence, it is necessary to find out whether pupil’s who enter Standard One have the same physical development levels and whether the age at which a pupil starts Standard One has an effect on the pupil’s performance in literacy and numeracy test. The study used a cross-sectional design in which an MDAT, Mathematics, English, Chichewa and EGRA tests were administered to 137 new entrants to Standard One in Thyolo district. The results of the study showed that older pupils are most developed and successively perform better in numeracy and literacy test than normal aged and under aged pupils. However under aged pupils are the least developed and poor performers in numeracy and literacy test. Based on the findings it was concluded that enrolling pupils in Standard One at the official entry age of 6 improves their performance in numeracy and literacy test scores.