The study examined the effect of meta-cognitive training on field-dependent and field-independent primary school pupils' knowledge of numeracy concepts. It also investigated the moderating effects of sex on meta-cognitive training of the two categories of learners on performance in numeracy. In addition, it investigated the moderating effects of sex on the outcome of meta-cognitive training of the two categories of learners' in a computer-mediated classroom on retention of learned numeracy concept. These were with a view to providing information on how meta-cognitive training affected numeracy achievement of Nigerian pupils' in computer-mediated classrooms. The study adopted the pretest, posttest, control group experimental design. The study population comprised primary school pupils and the sample comprised 39 primary three pupils from two schools in two educational zones. The schools were purposely selected because of availability of computer facilities in their schools. Three research instruments were used for this study namely: Meta-cognitive Training Manual (MCTM), Pupils' Achievement Test on Numeracy (PATON) (response instrument) and One treatment instrument which is Computer Numeracy Instructional Package for Primary School Children (CNIP[superscript 2] SC) (stimulus instrument). Data obtained were analyzed using descriptive and inferential statistics of Analysis of Covariance (ANCOVA). The results showed that meta-cognitive training had significant effect on performance of learned numeracy concepts of field-dependent and field-independent learners' (F = 11.16; p<0.05), sex had no significant effect on performance in numeracy between the groups of learners (F = 0.14; p>0.05). It was also obtained that there was no moderating effect of sex on retention of numeracy performance of the two categories of learners (F = 0.22; p >0.05).