The judgement time (RT) has been reported as inverse linear function of the logarithm of the estimated difference in size of the animals. A smaller size difference between animals is presumed to be represented as a smaller difference between their internal analogues resulting in decreased discriminability and increased judgement time. These findings were considered consistent with the dual coding theory. However, their developmental trends remain relatively less explored. Total 60 children 20 each in 5-7, 7-9 and 9-11 years age group participated in mental size comparison experiment. The results showed that pictorial material produced fastest judgement followed by mixed (pictorial + verbal) material which produced faster judgement than verbal material. The judgement latencies for all kinds of material decreased with age. However, the superiority of pictorial over verbal material sustained across different age levels of children. The findings were consistent with the prediction of Dual Coding Theory (Paivio, 1971, 1978).