In recent years, small-scale studies have suggested that we may be able to substantially strengthen children's general cognitive abilities and intelligence quotient (IQ) scores using a relational operant skills training program (SMART). Only one of these studies to date has included an active Control Condition, and that study reported the smallest mean IQ rise. The present study is a larger stratified active-controlled trial to independently test the utility of SMART training for raising Non-verbal IQ (NVIQ) and processing speed. We measured personality traits, NVIQs, and processing speeds of a cohort of school pupils (aged 12-15). Participants were allocated to either a SMART intervention group or a Scratch computer coding control group, for a period of 3 months. We reassessed pupils' NVIQs and processing speeds after the 3-month intervention. We observed a significant mean increase in the SMART training group's (final n[subscript exp] = 43) NVIQs of 5.98 points, while there was a nonsignificant increase of 1.85 points in the Scratch active-control group (final n[subscript cont] = 27). We also observed an increase in processing speed across both conditions (final n[subscript exp] = 70; n[subscript cont] = 55) over Time. Our results suggest that relational skills training may be useful for improving performance on matrices tasks, and perhaps in future, accelerating children's progression toward developmental milestones.