The current research aimed to know the effect of age and diagnosis (normal and those with attention deficit hyperactivity disorder) and the binary interactions between them on the performance of time-based prospective memory, the ongoing task, and time monitoring of primary school pupils, and to know the possibility of predicting the performance of time-based prospective memory from time monitoring. The basic research participants were (166) primary school pupils (72 normal ADHD and 94 with ADHD). The research instruments were a car driving task, and the attention deficit/hyperactivity test (Prepared by: Abdul Raqib Al-Bahri and Mustafa Al-Hadibi, 2021). A t-test, MANOVA, mixed factor analysis of variance, and multiple regression analysis were used. The results showed that there were statistically significant differences between normal and those with attention deficit hyperactivity disorder in time-based prospective memory and time monitoring in favor of normal pupils. There was also an effect of age on the performance of time-based prospective memory and time monitoring in favor of older primary school pupils (12-13 years). There was no effect of the binary between age and diagnosis on time-based prospective memory and time monitoring of primary school pupils. Time-based prospective memory performance could be predicted from time monitoring of primary school pupils.